Patent Publication Number: US-2022233871-A1

Title: External pulse generator device and affixation device for trial nerve stimulation and methods of use

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. Non-Provisional application Ser. No. 16/513,165, filed on Jul. 16, 2019, which is a continuation of U.S. Non-Provisional application Ser. No. 15/431,475, filed on Feb. 13, 2017, and issued as U.S. Pat. No. 10,376,704 on Aug. 13, 2019, which claims the benefit of priority to U.S. Provisional Application 62/294,639 filed Feb. 12, 2016, the entire contents of each which are incorporated herein by reference. 
     The present application is related to U.S. Non-Provisional application Ser. No. 14/827,081, entitled External Pulse Generator Device and Associated Methods for Trial Nerve Stimulation” filed on Aug. 14, 2015, the entire contents of which are incorporated herein by reference in its entirety for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     Treatments with implanted neurostimulation systems have become increasingly more common in recent years. While such systems have shown promise in treating a number of chronic conditions, effectiveness of treatment may vary considerably between patients and viability of treatment can be difficult to determine before implantation. Although conventional methods of implantation often utilize preliminary testing with a temporary, partly implanted neurostimulation systems to assess viability of treatment, such systems may not provide an accurate representation of treatment with a fully implanted device. In addition, such systems are often bulky, uncomfortable and limit patient mobility, such that many patients elect not to receive a temporary system or a fully implanted system. In addition, many such temporary partly implanted systems may not operate in the same manner as their fully implanted counterparts due to differences between pulse generators or changes in position of the neurostimulation leads during conversion. Therefore, it is desirable to provide methods and devices for providing trial treatment systems that provide a more accurate representation of treatment, improve patient comfort and provide consistent treatment outcomes as compared to fully implanted neurostimulation systems. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to neurostimulation treatment systems, and in particular a neurostimulation treatment system having an EPG with a multi-purpose connector receptacle and affixation devices on which the EPG is releasably mounted and that are secured to the patient during a trial neurostimulation treatment. Typically, such a trial neurostimulation treatment includes a partly implanted neurostimulation lead extending to an external pulse generator for conducting a trial neurostimulation treatment for assessing viability of a fully implanted system. In one aspect, the system includes a partly implanted neurostimulation lead that extends from one or more implanted neurostimulation electrodes to an external pulse generator (EPG) supported in an affixation device secured to the patient. In some aspects, the trial period may be as little as 4-7 days, while in other aspects the trial period may extend two weeks or more, typically about two weeks. 
     In one aspect, an external pulse generator is provided that includes an outer housing having at least one port and a connector receptacle accessed via the port. The receptacle can be adapted for receivably coupling with a proximal portion of an implantable neurostimulation lead to electrically couple the external pulse generator with one or more neurostimulation electrodes of the neurostimulation lead implanted at a target tissue. The external pulse generator further includes a pulse generator electrically coupled with the connector receptacle and adapted for generating neurostimulation pulses to one or more neurostimulation electrodes of the lead. The connector receptacle can be configured to support various types of neurostimulation lead, including a Peripheral Nerve Evaluation (PNE) lead (bilateral or unilateral) as well as a tined lead. The external pulse generator can further include a rechargeable battery electrically coupled to the pulse generator and connector receptacle that is configured for recharging by electrical power delivered via the connector receptacle. 
     In some embodiments, the external pulse generator can include electrical circuitry coupling each of the pulse generator, the rechargeable battery and the connector receptacle. The circuitry is configured, by programmable instructions recorded on a memory thereof, to power the pulse generator with the charged battery and charge the battery with electrical power delivered via the connector receptacle. The circuitry can further be configured to switch between differing operating modes of the external pulse generator, which can include a therapy mode and a charging mode. In some embodiments, the circuitry is configured to switch to the charging mode when the connector receptacle is coupled to power connector of a charging cord coupled to an external power source. The circuitry can also be configured to switch to the therapy mode when the connector receptacle is coupled to the proximal connector of the neurostimulation lead. The circuitry can further be adapted for suspending pulse generation in response to disconnecting the neurostimulation lead. Suspending pulse generation can be performed in response to a detection of loss of electrical connectivity within the connector receptacle while in the therapy mode. This capability serves as a safety feature and can be included in any EPG, including multi-port EPGs, regardless of whether a rechargeable or a permanent battery is used. 
     In some embodiments, an external pulse generators can include circuitry configured for switching to the charging mode by electrically connecting the battery to the receptacle while operatively disconnecting the battery from the pulse generator, and switching to the therapy mode by operatively connecting the pulse generator to the battery and electrically disconnecting the battery from the receptacle. In some embodiments, the external pulse generator includes one or more stimulation programs operable within the therapy mode for use in one or more trial stimulation periods. In some embodiments, the external pulse generator is reusable such that it can be reused in multiple trials and/or with multiple patients. These aspects allow for improved versatility and makes a trial nerve stimulation more accessible to a wide range of patient populations. 
     In another aspect, such a trial system can include an external pulse generator with a multi-purpose connector receptacle. Such an external pulse generator can be configured with a single connector receptacle. The connector receptacle can be adapted for alternatingly connecting with a plurality of differing connectors, which can include a proximal lead connector of a neurostimulation lead and a power connector of a charging cord. In some embodiments, the circuitry is adapted for charging the battery when the charging cord is electrically coupled with a standard 120 volt outlet. The differing types of connectors can further include multiple differing connectors associated with differing cable sets, each suited for a particular purpose. Such differing connectors can include a first connector on a proximal portion of the neurostimulation lead; a second connector coupled in parallel to each of a ground and one or more proximal connectors of one or more implantable neurostimulation leads each having one or more neurostimulation electrodes, typically one or two proximal connectors of one or two neurostimulation leads; a third connector coupled in parallel to two or more proximal connectors of neurostimulation leads; and a fourth connector coupled with a charging cord and adapted for use in charging a rechargeable battery of the external pulse generator. 
     In another aspect, methods of performing a neurostimulation treatment during a trial period are provided herein. Such a method can include, first, electrically coupling a neurostimulation lead to an external pulse generator, the lead including one or more neurostimulation electrodes implanted at or near a targeted tissue within the patient. The neurostimulation treatment can then be delivered to the one or more neurostimulation electrodes with the external pulse generator. To facilitate charging, a rechargeable battery of the external pulse generator can be electrically coupled with an external power source via the first receptacle port of the external pulse generator, after which the battery is charged with the external power source. In some embodiments, delivering the neurostimulation lead can be performed in a neurostimulation operating mode of the external pulse generator, while charging of the external pulse generator can be performed in a charging operating mode. Such methods can further include: switching to the neurostimulation mode upon connection of the neurostimulation lead; and switching to the charging mode upon connection of a charging cord connected to an external power source and/or grounding. 
     In yet another aspect, an external pulse generator affixation device for securing an external pulse generator on a patient is provided herein. Such affixation devices can include a substrate having a patient coupling feature disposed along a first side and a mounting portion disposed along a second side opposite the first side. The mounting portion can include a plurality of tabs that engage the external pulse generator along an outer perimeter thereof so as to releasably couple the external pulse generator with the substrate. The plurality of tabs can be dimensioned and arranged so that a majority of the outer perimeter remains exposed to allow a patient to readily detach the external pulse generator from the adhesive patch while coupled to the patient. In some embodiments, the tabs are dimensioned and arranged so that about ⅔ or more of the outer perimeter remains exposed, or so that about ⅘ or more of the outer perimeter remains exposed, or so that about 9/10 or more of the perimeter remains exposed. In embodiments where the EPG is of a substantially rectangular shape, the multiple tabs can be arranged such that at least two diagonally opposing corners, or even all four corners, of the substantially rectangular EPG are exposed so that the EPG can be removed by grasping and engaging the corners of the EPG while secured within the affixation device. 
     In some embodiments, the mounting portion is non-electrically conductive. Typically, the affixation device is without any electrodes or electrically conductive path by which stimulation can be delivered to a skin of the patient. 
     In some embodiments, the affixation device includes a mounting portion with multiple tabs that include at least two resiliently deflectable tabs, each having a retention feature that engages an outer housing of an external pulse generator so as to releasably secure the external pulse generator to the substrate. The retention features of each of the at least two deflectable tabs can be adapted to be received within corresponding retention features on opposite sides of the external pulse generator. In some embodiments, the retention features of each tab comprises a contoured or stepped portion of each tab and the retention feature of the external pulse generator includes a retention recess having a corresponding contour or stepped portion for receiving the retention features of the at least two tabs. When the external pulse generator is substantially rectangular in shape, the at least two resiliently deflectable tabs can be adapted to engage opposing sides of the external pulse generator along a length dimension of the external pulse generator. In some embodiments, the mounting portion can include at least two additional tabs that engage opposing sides of the external pulse generator along a width dimension. In some embodiments, the at least two deflectable tabs and/or the at least two additional tabs engage the external pulse generator along a mid-portion thereof so that the external pulse generator can be removed by grasping the exposed sides and/or corners and twisting the external pulse generator along one or more axes. 
     In some embodiments, the affixation device includes an EPG mounting portion with multiple tabs that include a first pair of deflectable tabs adapted to engage opposite sides of the external pulse generator along a first axis to constrain movement along the first axis and a second pair of deflectable tabs adapted to engage opposite sides of the external pulse generator along a second axis substantially orthogonal to the first axis to constrain movement along the second axis. The second pair of deflectable tabs can each include a retention feature that engages a corresponding retention feature of the external pulse generator to constrain movement along a third axis orthogonal to each of the first and second axis. In this aspect, the plurality of tabs, in combination, constrain movement of the external pulse generator relative the substrate in all three dimensions. The substrate can be substantially rigid or semi-rigid between the multiple tabs so as to maintain the relative position and orientations of the tabs. 
     In some embodiments, the patient coupling feature of the affixation device is a flexible adhesive patch having a pressure-sensitive adhesive with sufficient strength to support an external pulse generator mounted on the adhesive patch adhered to a skin of the patient. In other embodiments, the patient coupling feature is a clip having an elongate member extending along and separable from the substrate. The clip can be biased towards the substrate so that the device is securable by insertion of a portion of a garment or belt between the elongate member and the substrate. The elongate clip member can be pivotally coupled to the substrate and biased toward the substrate is loaded with a spring. 
     In another aspect, the EPG includes a pulse generator electrically configured for generating neurostimulation pulses along multiple stimulation channels, a battery electrically coupled to the pulse generator, an outer housing enclosing the pulse generator and battery, and a multi-pin connector electrically coupled with the pulse generator through an external cable extending from the housing. The multi-pin connector includes multiple pins that correspond to the multiple channels. In some embodiments, the external cable is permanently attached to the housing such that any electrical connections between the multi-pin connector and the pulse generator are permanently sealed. Typically, the external cable is between 1 inch and 12 inches in length. In some embodiments, the battery is non-removable by the patient. In some embodiments, the battery is non-rechargeable. 
     In some embodiments, the EPG includes an actuatable user interface feature, such as a button or switch, that is disposed on the housing and configured for initiating wireless communication with an external programmer when actuated. In some embodiments, the actuatable user interface is configured such that actuation while the pulse generator is off or in a hibernation state causes the EPG to be receptive to or initiate wireless communication with the external programmer for a pre-determined period of time, and operation or communication by the EPG remains unchanged when actuation occurs while the pulse generator is operating or communicating. The pre-determined period of time can be any suitable period of time, for example 30 seconds or more, typically about 60 to 90 seconds. In some embodiments, the EPG is configured such that if no communication is established with the external programmer during the pre-determined period of time, the EPG returns to a hibernation or off state. Typically, the EPG is wirelessly coupleable with a patient remote and configured to turn off stimulation during operation in response to a command received from the patient remote. 
     In some embodiments, the EPG further includes a status indicator interface disposed on the housing and configured to indicate status of: a communication between the EPG and an external programmer, an operating state, a battery level, an error state, or any combination thereof. In some embodiments, the EPG housing has opposing major faces, a contoured top surface and a flattened underside surface for placement against the patient when the EPG is worn during a trial period. In some embodiments, the status indicator interface and the actuatable user interface are disposed on the underside surface of the housing of the EPG. 
     In another aspect, the trial system includes an EPG having a multi-pin connector and multiple connectors selectively coupleable within the multi-pin connector. The multiple connectors including at least two of: a first connector on a proximal portion of the neurostimulation lead, a second connector coupled in parallel to each of a ground and one or more proximal connectors of one or more implantable neurostimulation leads, each having one or more neurostimulation electrodes on a distal portion thereof, and a third connector coupled in parallel to two or more proximal connectors of two or more neurostimulation leads. In some embodiments, the trial system includes one or more connector cables coupleable with the multi-pin connector and one or more neurostimulation leads. In some embodiments, the one or more connectors can include a lead extension cable extending between a corresponding multi-pin connector and at least one implantable lead connector having a receptacle configured for receiving a proximal lead connector of a fully implantable neurostimulation lead. In some embodiments, the one or more connectors include a multi-lead cable extending between a corresponding multi-pin connector and multiple lead connectors, each having a lead receptacle for coupling with a neurostimulation lead, and at least one ground connector for coupling with a ground patch. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments, are intended for purposes of illustration only and are not intended to necessarily limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a trial neurostimulation system having a partly implanted lead extending to an EPG patch adhered to the skin of the patient, in accordance with some embodiments of the invention. 
         FIGS. 2A and 2B  are example overviews of the neurostimulation system of  FIG. 1 . 
         FIG. 3A  is an alternative configuration of a trial neurostimulation system, in accordance with some embodiments. 
         FIG. 3B  is yet another alternative configuration of a trial neurostimulation system, in accordance with some embodiments. 
         FIG. 3C  is a detail of the neurostimulation system in  FIG. 3 . 
         FIGS. 4A-4C  are overhead and side views of an example EPG affixation patch, in accordance with some embodiments. 
         FIG. 5  illustrates an EPG and an associated schematic in accordance with some embodiments. 
         FIG. 6  shows a schematic of an EPG in accordance with some embodiments. 
         FIGS. 7A-7B  illustrate an alternative EPG in accordance with some embodiments. 
         FIG. 7C  shows an exploded view of the EPG in  FIGS. 7A-7B . 
         FIGS. 8A-8B  illustrate an EPG and affixation device for use in a trial neurostimulation system in accordance with some embodiments. 
         FIGS. 9A-9B  illustrate an EPG and affixation device for use in a trial neurostimulation system in accordance with some embodiments. 
         FIG. 10  illustrates an example EPG supported in a pouch of a belt for use in a trial neurostimulation system in accordance with some embodiments. 
         FIG. 11  illustrates an example EPG covered by an adhesive patch or tape for use in a trial neurostimulation system in accordance with some embodiments. 
         FIGS. 12A-12F  illustrate an example EPG and alternate connector cables adapted for varying uses in accordance with some embodiments. 
         FIG. 13  illustrates an alternative percutaneous extension cable in accordance with some embodiments. 
         FIG. 14  illustrates an alternative basic trial cable in accordance with some embodiments. 
         FIG. 15  schematically illustrates a use of a trial neurostimulation system utilizing an EPG affixation device in accordance with some embodiments. 
         FIGS. 16-17  illustrate methods of performing a trial neurostimulation therapy in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Neurostimulation has been used for many years to treat a variety of conditions, from chronic pain, to erectile dysfunction and various urinary dysfunctions. While neurostimulation has proven effective in many applications, effective therapy often relies on consistently delivering therapeutic activation by one or more neurostimulation electrodes to particular nerves or targeted regions with a pulse generator. In recent years, fully implantable neurostimulation have become increasingly more commonplace. Although such implantable systems provide patients with greater freedom and mobility, the neurostimulation electrodes of such systems are more difficult to adjust once they are implanted. The neurostimulation electrodes are typically provided on a distal end of an implantable lead that is advanced through a tunnel formed in a patient tissue. 
       FIG. 1  schematically illustrates a use of a trial neurostimulation system utilizing an EPG affixation device, in accordance with aspect of the invention. Such a trial neurostimulation system can be used to assess viability of a fully implantable neurostimulation system. Implantable neurostimulation systems can be used in treating patients with, for example, chronic, severe, refractory neuropathic pain originating from peripheral nerves or various urinary and bowel dysfunctions. Implantable neurostimulation systems can be used to either stimulate a target peripheral nerve or the posterior epidural space of the spine. An implantable neurostimulation system includes an implanted pulse generator, typically implanted in a lower back region. In some embodiments, the pulse generator can generate one or more non-ablative electrical pulses that are delivered to a nerve to control pain or cause some other desired effect. In some applications, the pulses having a pulse amplitude of between 0-1,000 mA, 0-100 mA, 0-50 mA, 0-25 mA, and/or any other or intermediate range of amplitudes may be used. One or more of the pulse generators can include a processor and/or memory adapted to provide instructions to and receive information from the other components of the implantable neurostimulation system. The processor can include a microprocessor, such as a microprocessor from Intel® or Advanced Micro Devices, Inc.®, or the like. An implantable pulse generator may implement an energy storage feature, such as one or more capacitors or a battery, and typically includes a wireless charging unit. 
     The electrical pulses generated by the pulse generator are delivered to one or more nerves and/or to a target location via one or more leads that include one or more neurostimulation electrodes at or near the distal end. The leads can have a variety of shapes, can be a variety of sizes, and can be made from a variety of materials, which size, shape, and materials can be dictated by the application or other factors. In some applications, the leads may be implanted to extend along the spine or through one of the foramen of the sacrum, such as shown in  FIG. 1 , such as in sacral nerve stimulation. In other applications, the leads may be implanted in a peripheral portion of the patient&#39;s body, such as in the arms or legs, and can be configured to deliver one or more electrical pulses to the peripheral nerve such as may be used to relieve chronic pain. 
     One or more properties of the electrical pulses can be controlled via a controller of the implanted pulse generator. In some embodiments, these properties can include, for example, the frequency, strength, pattern, duration, or other aspects of the timing and magnitude of the electrical pulses. These properties can include, for example, a voltage, a current, or the like. This control of the electrical pulses can include the creation of one or more electrical pulse programs, plans, or patterns, and in some embodiments, this can include the selection of one or more pre-existing electrical pulse programs, plans, or patterns. In the embodiment depicted in  FIG. 1 , the implantable neurostimulation system  100  includes a controller in the implantable pulse generator having one or more pulse programs, plans, or patterns and/or to select one or more of the created pulse programs, plans, or patterns. 
     Sacral neuromodulation (SNM), also known as sacral nerve stimulation (SNS), is defined as the delivery of mild electrical pulses to the sacral nerve to modulate the neural pathways controlling bladder and rectal function. This policy addresses use of SNM in the treatment of urinary or fecal incontinence, urinary or fecal nonobstructive retention, or chronic pelvic pain in patients with intact neural innervation of the bladder and/or rectum. 
     Treatment using SNM, also known as SNS, is one of several alternative modalities for patients with fecal incontinence, r overactive bladder (urge incontinence, significant symptoms of urgency-frequency) or nonobstructive urinary retention who have failed behavioral (e.g., prompted voiding) and/or pharmacologic therapies. Urge incontinence is defined as leakage of urine when there is a strong urge to void. Urgency-frequency is an uncontrollable urge to urinate, resulting in very frequent small volumes. Urinary retention is the inability to completely empty the bladder of urine. Fecal incontinence is the inability to control bowel movements resulting in unexpected leakage of fecal matter. 
     The SNM device consists of an implantable pulse generator that delivers controlled electrical impulses. This pulse generator is attached to wire leads that connect to the sacral nerves, most commonly the S3 nerve root. Two external components of the system help control the electrical stimulation. A patient remote control may be kept by the patient and can be used to control any of the variety of operational aspects of the EPG and its stimulation parameters. In one such embodiment, the patient remote control may be used to turn the device on or return the EPG to a hibernation state or to adjust stimulation intensity. A console programmer is kept by the physician and used to adjust the settings of the pulse generator. 
     In a conventional approach, prior to implantation of the permanent device, patients undergo an initial testing phase to estimate potential response to treatment. The first type of testing developed was percutaneous nerve evaluation (PNE). This procedure is done under local anesthesia, using a test needle to identify the appropriate sacral nerve(s). Once identified, a temporary wire lead is inserted through the test needle and left in place for 4 to 7 days. This lead is connected to an external stimulator, which can be carried by patients in their pocket, secured against the skin under surgical dressings, or worn in a belt. The results of this test phase are used to determine whether patients are appropriate candidates for the permanent implanted device. For example, for overactive bladder, if patients show a 50 percent or greater reduction in symptom frequency, they are deemed eligible for the permanent device. 
     The second type of testing is a 2-stage surgical procedure. In Stage 1, a quadripolar-tined lead is implanted (stage 1). The testing phase can last as long as several weeks, and if patients show a specified reduction in symptom frequency, they can proceed to Stage 2 of the surgery, which is permanent implantation of the neuromodulation device. The 2-stage surgical procedure has been used in various ways. These include its use instead of PNE, for patients who failed PNE, for patients with an inconclusive PNE, or for patients who had a successful PNE to further refine patient selection. 
     In one aspect, the duration of battery life of the EPG is at least four weeks for a tined lead at nominal impedance (e.g. about 1200 Ohms), an amplitude of about 4.2 mA, and a pulse width of about 210 us, or the duration of battery life can be at least seven days for a PNE lead. In some embodiments, the battery is rechargeable and can be recharged by coupling the battery with a standard 120 V wall outlet, and may optionally utilize the same power cables or adapter as used by other system components (e.g. clinician programmer). Typically, the EPG is current controlled. The EPG can be configured with a pulse width between 60-450 μs, a maximum stimulation rate between 2 and 130 Hz, a maximum amplitude between 0 and 12.5 mA, a stimulation waveform that is biphasic charge-balanced assymetric, minimum amplitude steps of about 0.05 mA, continuous or cycling operating modes, a set number of neurostimulation programs (e.g. two programs), ramping capability, and optional alert built into the EPG. 
     The permanent device is implanted under local or general anesthesia. An incision is made over the lower back and the electrical leads are placed in contact with the sacral nerve root(s). The wire leads are extended underneath the skin to a pocket incision where the pulse generator is inserted and connected to the wire leads. Following implantation, the physician programs the pulse generator to the optimal settings for that patient. 
     One example of a common process for treating bladder dysfunction is to employ a trial period of sacral neuromodulation with either a percutaneous lead or a fully implanted lead in patients that meet all of the following criteria: (1) a diagnosis of at least one of the following: urge incontinence; urgency-frequency syndrome; non-obstructive urinary retention; (2) there is documented failure or intolerance to at least two conventional therapies (e.g., behavioral training such as bladder training, prompted voiding, or pelvic muscle exercise training, pharmacologic treatment for at least a sufficient duration to fully assess its efficacy, and/or surgical corrective therapy); (3) the patient is an appropriate surgical candidate; and (4) incontinence is not related to a neurologic condition. 
     Permanent implantation of a sacral neuromodulation device may be considered medically necessary in patients who meet all of the following criteria: (1) all of the criteria (1) through (4) in the previous paragraph are met; and (2) trial stimulation period demonstrates at least 50% improvement in symptoms over a period of at least one week. 
     Other urinary/voiding applications of sacral nerve neuromodulation are considered investigational, including but not limited to treatment of stress incontinence or urge incontinence due to a neurologic condition, e.g., detrusor hyperreflexia, multiple sclerosis, spinal cord injury, or other types of chronic voiding dysfunction. (See policy description of sacral nerve neuromodulation/stimulation coverage provided by Blue Cross Blue Shield available online at: http://www.bcbsms.com/com/bcbsms/apps/PolicySearch/views/ViewPolicy. php?&amp;noprint=yes&amp;path=%2Fpolicy%2Femed%2FSacral_Nerve_Stimulation.html) 
     In another conventional approach, a similar method is used in peripheral neurostimulation (PNS) treatment systems. Generally, candidates for peripheral neurostimulation are assessed to determine their suitability for undergoing the PNS procedure. Prior to the surgery, the patient will undergo pre-surgical testing that includes routine blood tests as well as neuropsychological evaluation. The PNS procedure itself is typically performed in two separate stages. Each stage takes about one hour, and the patient can go home the same day. 
     In this aspect, Stage 1 involves implanting of trial electrodes, via small needles, which are connected to an external pulse generator (EPG), typically worn on a belt of the patient. A number of stimulation programs are administered over the next few days. If this trial demonstrates a significant improvement in the patient&#39;s headache or facial pain, permanent implantation can take place. In Stage 2, a new set of electrodes, the width of angel-hair pasta, are implanted under the skin. These are connected to a smaller implantable pulse generator implanted under the skin in the chest, abdomen, or back. 
     Among the drawbacks associated with these conventional approaches, is the discomfort associated with wearing an EPG. The effectiveness of a trial period such as in PNE and Stage 1 trial periods are not always indicative of effective treatment with a permanent implanted system. In one aspect, since effectiveness of treatment in a trial period may rely, in part, on a patient&#39;s subjective experience, it is desirable if the discomfort and inconvenience of wearing an EPG by the patient can be minimized so that the patient can resume ordinary daily activities without constant awareness of the presence of the EPG and treatment system. This aspect can be of particular importance in treatment of overactive bladder and erectile dysfunction, where a patient&#39;s awareness of the device could interfere with the patient&#39;s experience of symptoms associated with these conditions. 
     In one aspect, the invention allows for improved assessment of efficacy during trial periods by providing a trial system having improved patient comfort so that patients can more easily recognize the benefits and effectiveness of treatment. In another aspect, the portions of the EPG delivering the therapy are substantially the same as the IPG in the permanent system such that the effects in permanent treatment should be more consistent with those seen in the trial system. 
     In certain embodiments, the invention provides an EPG patch worn on a skin of the patient so as to improve patient comfort. Optionally, the EPG used in Stage 1 may be smaller than the IPG used in the corresponding Stage 2 so that the EPG can easily be supported by and sealed against contamination by an adherent patch that covers the EPG. In one aspect, the EPG is a modified version of the implantable IPG used in Stage 2. The IPG may be modified by removal of one or more components, such as removal of a remote charging coil with a smaller battery and associated components. In addition, the EPG may use a thinner, lighter housing than the IPG, since the EPG is not required to last for many years, such as the IPG would be. The EPG therefore, may be configured to be disposable. These aspects allow the EPG to be supported within a patch adhered to the skin of the patient at a convenient and comfortable location. 
       FIG. 1  illustrates an example trial neurostimulation system  100  having an EPG patch  10 . As shown, the neurostimulation system is adapted to stimulate a sacral nerve root. The neurostimulation system  100  includes an implantable pulse generator (IPG) implanted in a lower back region, from which a neurostimulation lead  20  extends through a foramen of the sacrum to electrodes (not shown) disposed near the sacral root. The neurostimulation lead  20  further includes an anchor  10  disposed on a dorsal side of the sacrum. It is appreciated, however, that the anchor may be disposed on a ventral side of the sacrum as well, or within the foramen itself. In one aspect, the EPG  40  is disposable and discarded after the trial is complete. Typically, the trial may last anywhere from 4 days to 8 weeks. Typically, an initial assessment may be obtained after 4-7 days and, if needed, effectiveness of treatment may be examined after a few weeks, typically about 2 weeks. In one aspect, the EPG  40  of the EPG patch  10  is of a substantially similar design as the IPG that would be implanted if the trial proves successful, however, one or more components may be removed to allow the EPG to be smaller in size, lower in mass, and/or differing materials are used since the device may be intended for one time use. 
       FIG. 2A  shows an embodiment of neurostimulation system  100 , similar to that in  FIG. 1 , in more detail. As can be seen, the neurostimulation lead  20 ′ includes a neurostimulation electrode  30  at a distal end configured for PNE use. The EPG  40  is supported within an adherent patch  11  when attached to a skin of the patient. 
       FIG. 2B  illustrates an alternate embodiment of neurostimulation system  100 , similar to that in  FIG. 1 , in more detail. Neurostimulation lead  20  is attached to EPG  40  via extension cable  22  and connector  21 . As can be seen, the neurostimulation lead  20  includes a plurality of neurostimulation electrodes  30  at a distal end of the lead and an anchor  50  having a plurality of tines disposed just proximal of the electrodes  30 . Typically, the anchor is disposed near and proximal of the plurality of electrodes so as to provide anchoring of the lead relatively close to the electrodes. The EPG  40  is supported within an adherent patch  11  when attached to a skin of the patient. 
     In one aspect, additional adherent patches  16  may be used to cover and seal the percutaneous incision in the skin of the patient through which the percutaneous portion of the neurostimulation lead is inserted. The lead may be secured at the percutaneous incision with surgical tape  17  and further secured and sealed with an adherent patch covering the lead and percutaneous incision. In this manner, the percutaneous incision can be sealed and protected from contamination or infection and its position maintained by the additional adherent patches  16 . This configuration reduces the likelihood of infection and prevents movement of the lead, both internal and external, such that the patient&#39;s awareness of the patch and lead is minimized, thereby allowing the patient to resume relatively normal daily activities. 
     In another aspect, since the EPG patch may be worn in a different location, such as on the abdomen, than the IPG would be implanted, to allow the IPG to use the same fully implanted neurostimulation lead  20 , the system may use a lead extension  22  coupled with the lead  20  by an implanted connector  21 . The lead extension  22  may optionally be hardwired into the EPG so as to eliminate potential disconnection and allow the connection to be sealed or encapsulated within the adherent patch so as to be water resistant or water proof. This allows the patient to perform routine daily activities, such as showering without removing the device. The length of lead  20  may be a suitable length for the permanently implanted system, while the length of extension  22  allows the lead to EPG patch to be positioned in a location that provide improved comfort and minimized interference with daily activities. 
       FIG. 3A  illustrates an alternate configuration in which the lead is sufficiently long to allow the EPG patch  10  to be placed to allow the patient more mobility and freedom to resume daily activities that does not interfere with sitting or sleeping. Excess lead can be secured by an additional adherent patch  16 , as shown by the center patch in  FIG. 3A . In one aspect, the lead is hardwired to the EPG, while in another the lead is removable connected to the EPG through a port or aperture in the top surface of the flexible patch  11 . In one aspect, the EPG patch and extension cable are disposable such that the implanted lead can be disconnected and used in a permanently implanted system without removing the distal end of the lead from the target location. In another aspect, the entire trial system can be disposable and replaced with a permanent lead and IPG. 
     In one aspect, the EPG unit may be wirelessly controlled by a patient remote in a similar or identical manner as the IPG of a permanently implanted system would be. The physician may alter treatment provided by the EPG through use of a portable clinician unit and the treatments delivered are recorded on a memory of the device for use in determining a treatment suitable for use in a permanently implanted system. 
       FIG. 3B  illustrates an alternate configuration in which the lead  20  is connected to a lead extension  21  through a connector  21 . This allows for the implanted lead to be used for both the trial and permanent system. This also allows the lead  20  of a length suitable for implantation in a permanent system to be used. Three access locations are shown: two percutaneous puncture sites, one for the lead implantation over the sacral area, and one for the extension exit site, while in between the puncture locations an incision (&gt;1 cm) is made for the site of the connection of the lead  20  and the extension cable  22 . 
     This approach minimized movement of the implanted lead  20  during conversion of the trial system to a permanently implanted system. During conversion, the lead extension  22  can be removed along with the connector  21  and the implanted lead  20  attached to an IPG that is placed permanently implanted in a location at or near the site of the first percutaneous incision. In one aspect, the connector  21  may include a connector similar in design to the connector on the IPG. This allows the proximal end of the lead  20  to be coupled to the lead extension  22  through the connector  21  and easily detached and coupled to the IPG during conversion to a permanently implanted system. 
       FIG. 3C  illustrates a detailed view of an EPG patch adhered to the skin of the patient, an additional adherent patch  16  disposed over the percutaneous incision through the lead extends into the patient and another additional patch  16  covering a loop of excess lead, the patch overlapping the first additional patch and the edge of the EPG patch  10 . This configuration is advantageous as it substantially covers and seals the EPG and the lead from contamination and prevents accidental disconnection or migration of the lead by the patient, and streamlines the external portions of the system so as to improve patient comfort and allow a patient&#39;s subjective experience to more closely match what the patient would experience in a permanently implanted system. 
       FIGS. 4A-4C  illustrates an overhead view and side views of an embodiment of EPG  40  that is smaller than a subsequently used IPG. Such an EPG can be situated within an EPG adherent patch affixation device  10 , or in any other affixation device described herein. In one aspect, the EPG is smaller than the IPG in the corresponding fully implantable permanent system. In certain embodiments, the outside width (w 2 ) of the adherent patch  11  is between 2 and 5 inches, preferably about 2.5 inches, while the outside length (l 2 ) of the patch  11  is between 3 and 6 inches, preferably about 4 inches; the width of the EPG (w 1 ) is between 0.5 and 2 inches, preferably about 1 inch, while the length (l 1 ) is between 1 and 3 inches, preferably about 2 inches; and the thickness (t) of the entire EPG patch  10  is less than 1 inches, preferably 0.8 inches or less. This design is considerably smaller than EPGs in conventional systems and thus interferes less with the daily activities of the patient during the trial period. The above described dimensions can be applicable to any of the embodiments described herein. Although in this embodiment, adherent patch  11  encapsulates the EPG within an interior cavity, it is appreciated that the EPG could be coupled with an adherent patch in any number of ways, including use of various coupling features. In some embodiments, the EPG is supported within a pouch of a belt or covered by an adhesive patch or surgical tape. In some embodiments, such as those described below, such coupling features can be configured to allow for ready removal of the EPG from the affixation device. 
     The underside of the adherent patch affixation device  11  is covered with a skin-compatible adhesive. The adhesive surface may be configured with any adhesive or adherent material suitable for continuous adhesion to a patient for the direction of the trial period. For example, a breathable strip having skin-compatible adhesive would allow the patch  12  to remain attached to the patient continuously for over a week, typically two weeks to four weeks, or even longer. These aspects can be included on any of the affixation devices described herein that couple to the patient by means of an adhesive surface. 
       FIG. 5  illustrates an example EPG  40  for use in a neurostimulation trial in accordance with various aspects of the invention. EPG  40  includes a substantially rigid outer shell or housing  41 , in which is encased a stimulation pulse generator, a battery and associated circuitry. EPG  40  also includes a connector receptacle  42  accessed through an opening or port in the outer housing  41  and adapted to electrically connect with a proximal lead connector  24  of a neurostimulation lead  20 ′. Although EPG  40  is shown connected with neurostimulation lead  20 ′, lead  20 , cables  22 , 26 , and  27  may also be connected to EPG  40 . Connector receptacle  42  includes multiple electrical contacts (e.g. six contact pins, eight-contacts pins), all or some of which can be connected to corresponding contacts points on a connector coupled thereto, depending on the type of connector. Connector receptacle  42  could be configured according to varying types of connector standards beyond that shown, for example, a USB or lightning cable connector. Lead connector  24  can include a proximal plug or boot  25  that sealingly engages the port when lead connector  24  is matingly connected within connector receptacle  42  to further secure the mated connectors and seal the port from intrusion of water, humidity or debris. Boot  25  can be formed of a pliable material, such as an elastomeric polymer material, that is fitting received within the port so as to provide ingress protection. In some embodiments, this configuration provides an ingress protection rating (IPR) is provided at IP24 or better. In this embodiment, connector receptacle  42  includes multiple electrical contacts, each operatively coupled with the stimulation pulse generator, so that the EPG can deliver neurostimulation pulses to multiple neurostimulation electrodes of the lead when coupled to the connector receptacle  42 . 
     In one aspect, EPG  40  is configured with a multi-purpose connector receptacle  24 . For example, connector receptacle  42  can be coupled with either a neurostimulation lead  20 ′ as described above, or can be coupled with a power connector of a charging cord to allow recharging of an internal battery of EPG  40 . Such a configuration is advantageous as it allows the EPG housing  41  to be designed with a single opening or access port, which further reduces the potential exposure of internal components to water and debris, since the port is sealingly occupied by the lead connector during delivery of therapy during the trial period. In contrast, a device having a separate charging port would likely either remain open or may require use of a removable plug or cover to seal the additional port. EPG  40  can further be configured with multiple operating modes, each mode suited for a different purpose for which connector receptacle  42  can be used. Such modes can include a therapy operating mode in which the stimulation pulse generator of EPG  40  delivers stimulation pulses to the neurostimulation lead connected to connector receptacle  24 , and a charging mode in which a rechargeable battery within EPG  40  receives power. In some embodiments, EPG  40  includes only two operating modes, the therapy mode and charging mode. In other embodiments, EPG  40  can include various other operating modes, including but not limited to, various testing modes, a dual lead mode, a bipolar mode, and a monopolar mode. Such modes can correspond to differing connectors of a specialized cable set, such as any of those shown in  FIG. 12B-12F . 
     EPG  40  can further include an indicator  44 , such as an LED, that indicates a status of the EPG  40 , which can include an ON/OFF state, a hibernation state, a mode, or a charge state (e.g. “charging needed,” “low”, “fully charged”, “charging”). In some embodiments, indicator  44  is configured with differing colored LEDs that indicate differing states by displaying different colors. For example, a red light output can indicate “charging needed”, an orange light output can indicate “low” charge, and a green light output can indicate a “fully charged” status). Differing modes or status of EPG  40  could also be indicated by use of multiple lights or flashing or blinking patterns (e.g., flashing green indicates the EPG is “charging”). 
     In another aspect, EPG  40  is designed as a substantially planar polygonal prism having parallel major surfaces that are positioned flat against the patient&#39;s body when affixed to the patient during the trial period, such as the rectangular prism shown in  FIG. 5 . In this embodiment, EPG  40  is a substantially rectangular shape with rounded corners and curved edges, the x-axis extending along a lengthwise direction of the rectangle, they-axis extending along a widthwise direction of the rectangle and the z-axis (not shown) extending along a thickness direction. As shown, the corners and edges are rounded or chamfered for improved patient comfort when worn against the patient&#39;s abdomen or on the patient&#39;s belt. While a substantially rectangular shape with rounded edges is depicted here, it is appreciated that EPG  40  can be formed in various other shapes (e.g. circular, triangular, square, symmetrical or non-symmetrical shapes), and still be suited for use with affixation devices according to the principles described herein. 
       FIG. 6  shows a schematic of the example EPG  40  having a multi-purpose connector receptacle  42 . EPG  40  includes the stimulation pulse generator  46  and rechargeable battery  48  each coupled to connector receptacle  42  via associated circuitry  47  that controls delivery of power to and from the rechargeable battery  48  and the stimulation pulse generator  46  and connector receptacle  42 . Circuitry  47  can include one or more processors, controllers and a recordable memory having programmable instructions recorded thereon to effect control of the stimulation pulse generation, rechargeable battery discharge and charging, and indicator  44 . In some embodiments, memory includes pre-programmable instructions configured to effect multiple different operating modes, for example the therapy mode and charging mode. In the therapy mode, circuitry  47  uses the rechargeable battery  48  to power the stimulation pulse generator  46 , which produces stimulation pulses that are delivered to a connected neurostimulation lead via the connector receptacle  42 . In the charging mode, circuitry  47  controls delivery of power delivered via the connector receptacle  42  to rechargeable battery  48 . In some embodiments, circuitry  47  includes a controller that switches between differing modes, which can be effected upon connection of a certain connector types into connector receptacle  42 . For example, in some embodiments, EPG  40  can include a detector that can detects a certain type of connector (e.g. lead connector, charging connector). In other embodiments, a connector type can be determined by measurement or detection of electrical characteristics of the connection. For example, a charging connection may require electrically connectivity with only a certain number of electrical contacts (e.g. one, two, etc.) and a ground, while a neurostimulation lead may connect with all of the designated electrical contacts without any grounding required. In some embodiments, the mode can be set be manually or wirelessly set by a user as needed. 
     In some embodiments, EPG  40  is configured to suspend generation of stimulation pulses upon disconnection of any connector within the connector receptacle. Configuring the EPG with a detachable cable improves safety of the device by preventing stimulation pulse output through the connector receptacle if the neurostimulation lead or associated cable should become accidentally caught and dislodged or intentionally removed by the user. This aspect may be effected by detection of a loss of connectivity or any other means of determining that the connector has been removed. In other embodiments, the EPG does not include any built-in cable, but can include one or more connectors that allow the patient to readily attach and detach cables as needed. 
     In another aspect, trial neurostimulation system  100  includes an affixation device that secures EPG  40  to the patient while connected to a neurostimulation lead implanted at a target tissue within the patient. Typically, the affixation device is configured to secure the EPG on a mid-portion (e.g. lower back region) or hip of the patient, either through an adherent patch applied directly to a skin of the patient or a clip device that can be releasably attached to a garment of the patient. Various examples of differing types of affixation devices are described herein. 
     In one aspect, such an affixation device can be configured to allow the user to readily remove the EPG device. Such a configuration may be useful for certain activities, such as bathing or sleeping, and can improve patient compliance during the trial period. When patients are subjected to a trial therapy in which an EPG is fixedly secured to the skin with an adhesive patch, some patients may find the presence of the EPG to be too invasive or uncomfortable to continue with the trial, which prevents a determination of the suitability of neurostimulation therapy and greatly reduces the likelihood that the patient will proceed with a fully implanted system, even though the fully implanted system would not present the same discomfort. Therefore, providing an affixation device that secures the EPG to the patient but still allows for ready removal of the EPG (assuming a removable, detachable EPG) can further improve the success rate of the trial period and improve determinations of whether a patient is a candidate for a permanently implanted neurostimulation system. 
       FIGS. 7A-7B  illustrate an alternative EPG  50  that includes a housing  51  from which a short cable connector  52  extends to a lead connector  53 . In this embodiment, lead connector  53  is a multi-pin connector suitable for electrically connecting to a neurostimulation lead having multiple electrodes through an intermediate adapter or lead extension cable (see  FIG. 13 ). Typically, cable connector  52  is relatively short, for example a length between 1 and 12 inches, preferably 3 and 6 inches. In this embodiment, the multi-pin connector is a 4-pin connector suitable for connecting to a neurostimulation lead having four electrodes, however, it is appreciated that lead connector could include differing numbers of pins so as to be suitable for connection with neurostimulation leads having greater or fewer neurostimulation electrodes. In other embodiments, the lead connector can be configured with a receptacle  42  for connecting with a proximal lead connector of a neurostimulation lead, such as described previously in other embodiments. The EPG can be used with a tined lead trial or a temporary lead (PNE lead) trial. Configuring the connection to the lead external of the housing allows the EPG to be even smaller and lighter than those with the connection integrated within the device. Such a configuration also allows for some movement for adjustment or handling of the EPG while minimizing movement of the proximal lead connector, which can be secured by tape to the patient&#39;s body just proximal of the connector. 
     In some embodiments, the short cable connector  52  or “pigtail connector” is integrated with the EPG such that the electrical connections between the cable and the internal electronics of the EPG are permanently attached and sealed. This allows the EPG to further withstand intrusion of fluids and moisture during the trial stimulation period. 
     Depending on the selection of cables desired for use, the EPG may be used with a PNE lead (which may have one or more than one electrode and conductor), or a permanent lead. In addition, the EPG may be used for bilateral stimulation (the use of two leads, one for each for a patient&#39;s left and right sides) when a bilateral connector cable is used between the EPG and leads. 
     In some embodiments, the EPG includes a non-rechargeable single-use power source (e.g. battery) having sufficient power for operation of the EPG for at least the duration of the trial period (e.g. days, weeks, months). In such embodiments, the power source can be integrated and non-removable or non-replaceable by the patient. 
     As can be seen in  FIG. 7B , EPG housing  51  can be defined as two interfacing shells, top shell  51   a  defining the outer major surface and a majority of the side surfaces and bottom shell  52   b  defining an underside surface. In this embodiment, EPG has a substantially rectangular (e.g. square) prism with rounded edges. The top major surface can be shaped with a slightly convex contour, while the underside includes a substantially flattened surface for placement against the patient. Typically, the interfacing shells  51   a ,  52   b  are formed of a rigid or semi-rigid material, such as hardened polymer, so as to protect and seal the electronics within. 
     As shown in the exploded view of  FIG. 7C , EPG  50  includes top housing shell  51   a , compressible foam sheet  56   a , battery  57 , double-sided adhesive disc  56   b , short electrical connector cable  52 , printed circuit board  58 , O-ring  51   c  for sealing top housing shell  51   a  with bottom shell  51   b , and serial number label  59   a  and outer label  59   b , which are affixed to the underside of bottom shell  51   b . It is appreciated that this arrangement of elements is exemplary and various other arrangements are within the scope of the invention. 
     In some embodiments, the EPG includes one or more user interface features. Such user interface features can include any of a button, switch, light, touch screen, or an audio or haptic feature. In the embodiment shown in  FIGS. 7A-7B , EPG  50  includes a button  55  and an LED indicator  54 . Button  55  is configured to turn EPG  50  on from an off or hibernation state. When turned on, EPG can communicate with an external device, such as a clinician programmer to receive programming instructions, and can deliver stimulation to a connected neurostimulation lead while in an operating state. While button  55  can be used by the patient to turn EPG  50  on, it is appreciated that this functionality can be concurrent with any other functionality described herein. For example, EPG  50  can be further configured to be turned on from an off or hibernation state by use of a patient remote or can be configured to suspend delivery of stimulation upon detachment of the neurostimulation lead. It is appreciated that while a button is described in this embodiment, any actuatable user interface feature could be used (e.g. switch, toggle, touch sensor) that is typically actuatable between at least two states. 
     In this embodiment, EPG  50  is configured such that pressing button  55  turns on a communication function of the EPG. Once actuated, the EPG has a pre-determined period of time (e.g. 60 seconds, 90 seconds) to wirelessly connect to an external programmer (e.g. Clinican Programmer). If the EPG connects to the clinician programmer, the EPG stays on to facilitate programming and operating to deliver of stimulation per programming instructions. If connection is not successful, the EPG automatically turns of. If button  50  is pressed when EPG is on, nothing happens and the communication or operating remains unchanged. If a patient desires to turn off stimulation, the patient remote could be used or alternatively, detachment of the neurostimulation lead could also suspend stimulation. Since subsequent pressing of button  55  during operation does not turn the EPG to the off or hibernation state, the button can be positioned on an underside of the EPG that is placed against the patient when worn during the trial stimulation period, although it is appreciated that the button could be disposed anywhere on the housing of the EPG. Thus, in this embodiment, the functionality of button  55  facilitates initial programming during set-up of the trial period or for reprogramming, but does not require interaction by the patient during the trial period. Typically, control or adjustment of stimulation by the patient would be performed by use of the patient remote. In some embodiments, the EPG is provided in a hibernation mode and communication can be initiated by actuation of a button on the EPG to facilitate programming with the CP. In some embodiments, when the patient remote is used to turn stimulation off, the EPG returns to the hibernation state and only the CP can fully turn the EPG to an off-state. 
     In this embodiment, EPG  50  further includes a LED indicator  54  that indicates a status of the EPG. The status can include a status of communication between the EPG and a programmer device, a battery status, an error status, or any combination thereof. LED indicator  54  can be configured with differing colors or blinking patterns to indicate differing status. For example, the EPG can be configured such that a flashing green light indicates communication is on; a solid green light indicates EPG is in operating mode and the battery is good; a solid orange or yellow indicates battery is at an acceptable charge; a flashing orange or yellow indicates the battery is low; and a red light indicates an error state. Since the information conveyed by the EPG may be more suited for use by the clinician, LED indicator  54  can be situated on an underside of the EPG placed against the patient when worn during the trial period, although it is appreciated that the LED could be disposed anywhere on the housing of the EPG. 
       FIGS. 8A-8B and 9A-9B  illustrate examples of affixation devices that secure the EPG to the patient while still allowing for ready removal.  FIGS. 8A-8B  illustrate an adherent patch affixation device  11  and  FIGS. 9A-9B  illustrate an adjustable clip affixation device  12 . Each of these figures shows lead  20 ′ by way of example, however, any lead capable of connecting to the EPG may be used, for example lead  20 ,  22 ,  26 , or  27  may also be used. 
       FIG. 8A  illustrates adherent patch affixation device  11  before mounting of EPG  40  thereto. Adherent patch affixation device  11  includes a support substrate  13  that includes a patient coupling portion on a first side and an EPG mounting portion on a second, opposite side. Typically, the mounting portion is formed of a non-electrically conductive material, such as an insulative polymer material such that the affixation device is without any separate electrodes or electrically conductive path for delivering stimulation directly to the skin of the patient. In this embodiment, the patient coupling portion includes an adhesive patch  11   a  disposed along a major surface of the first side of the substrate. Adhesive patch  11   a  typically includes a flexible breathable material having a pressure sensitive adhesive suitable for securing to a skin of the patient for an extended duration of time, for example, for part or all of the trial period. While the adhesive patch  11   a  may be flexible and breathable for patient comfort, support substrate  13  is typically substantially rigid or semi-rigid so as to support one or more EPG mounting features and maintain the EPG mounted thereto. In this embodiment, the EPG mounting portion includes multiple outwardly extending tabs that engage an outer housing of the EPG along an outer perimeter, typically at least one tab on each major side of the EPG or distributed about the perimeter of the EPG housing. 
     As shown in  FIGS. 8A-8B , the multiple tabs can include two pairs of tabs. A first pair of tabs  14  are adapted to engage opposite sides of EPG  40  along the widthwise direction, while a second pair of tabs  15  engage opposite sides of EPG  40  along the lengthwise direction. In this embodiment, the second pair of tabs are resiliently deflectable to outwardly deflect upon pressing EPG  40  in between tabs  15  so that tabs  15  retain EPG  40  therebetween. EPG  40  can further include corresponding coupling features that fittingly engage each of the pairs of tabs  14 ,  15 . For example, EPG  40  can include recessed notches (not visible) that fittingly receive the first pair of tabs  14 . When fitted within corresponding recessed, the first pair of tabs  14  can constrain movement of EGP  40  in both x and y directions. EPG  40  can further include retention features that engage corresponding retention features of the mounting portion of the affixation device. For example, the second pair of tabs  15  can be defined with an inwardly curved, contoured or stepped-in portion that fits within a correspondingly shaped retention recess  45  within the lengthwise sides of EPG  40 . When the second pair of retention tabs  15  are resiliently received within retention features  45 , the second pair of tabs further constrains movement of EPG  40  in a z-direction, as well as the x and y-directions. Thus, in combination, the first and second pair of tabs secure and support EPG  40  within the affixation device in a particular orientation so that the proximal lead connector  24  can be securely maintained within lead connector receptacle  42 . 
     In another aspect, the multiple tabs can be dimensioned so that a majority of an outer perimeter of EPG  40  remains exposed so that a patient can readily grasp outer edges of EPG  40  and remove from the affixation device as needed. By leaving a majority of the perimeter exposed, this configuration allows the patient to grasp the EPG for ready release even when the EPG is affixed in a lower back region, where the patient cannot readily view the device during detachment. In some embodiments, the multiple tabs are dimensioned so that ¾ or more of the perimeter of EPG  40  remains exposed. In other embodiments, the multiple tabs are dimensioned so that ⅘ or more, or even 9/10 or more of the outer perimeter is exposed, so as to further facilitate ready grasping by the patient to facilitate ready removal. In some embodiments where EPG  40  is substantially rectangular in shape, such as in the embodiment of  FIG. 8A , the multiple tabs are configured to engage each side of EPG  40  at or near a mid-portion. This configuration allows for improved support and retention of EPG  40  while allowing at least two diagonally opposed corners, typically all four corners, to remain exposed. This arrangement allows the patient to effect release by grasping the edges and/or corners of EPG  40  and twisting along one or more axis (x, y or z) so as to release the second pair of retaining tabs  15  from corresponding retention recesses  45  for ready removal of EPG  40 . The patient can then detach lead connector  24  from connector receptacle  42  and charge or store EPG  40  as needed. 
       FIG. 9A  illustrates a spring-clip affixation device  12  for releasably securing EPG  40  to the patient. Affixation device  12  includes a substantially rigid or semi-rigid support substrate  13  having a patient coupling portion (e.g. spring-clip) on one side and an EPG mounting portion with one or more coupling features on an opposite side. Similar to the embodiment in  FIG. 8A , the EPG mounting portion includes two pairs of tabs, a first pair of tabs  14  and a second pair of tabs  15  with retention features, each pair of tabs adapted to fittingly engage with corresponding features in the outer housing  41  of EPG  40  so as to securely mount EPG  40  to the substrate while allowing the patient to grasp and readily release EPG  40  from the affixation device  12 , as described above with respect to the embodiment of  FIG. 8A . In this embodiment, the patient coupling feature includes clip  16  that extends along the backside of substrate  13  and is separable from and biased towards substrate  13  so that a piece of the patient&#39;s garment or belt can be inserted therebetween. In this embodiment, clip  16  is pivotally coupled to substrate by a pivotal coupling  17  that is loaded with a spring to bias clip  16  towards the substrate. Clip  16  can further include a grasping feature  18  on an outer facing surface near a base of clip  16  so that the patient can readily grasp clip  16  and remove the clip by pressingly engaging the base and separate clip  16  from substrate  14  to release the garment or belt from the clip. Alternatively, the patient could grasp and release EPG  40  from the mounting portion of the clip affixation device  12 , as described above, while leaving the clip  16  attached to the belt or garment. Typically, substrate  13  and clip  16  are formed of a substantially rigid or semi-rigid formable material, such as plastic. Clip  16  can be further configured to fit into a specialized belt. 
     In another aspect, any of the EPG devices described herein can be supported by an adherent patch, as described previously, or can be supported by various affixation devices, such as any of those described. For example, as shown in  FIG. 10 , EPG  50  can be supported in a pouch  61  of an adjustable belt  60  worn by the patient. Pouch  61  can be formed of a flexible compliant or non-compliant material to improve patient comfort during the trial period. Alternatively, as shown in  FIG. 11 , EPG  50  can be supported by covering the EPG with an adhesive patch  16  or surgical tape. Since, in some embodiments, the EPG does not require patient interaction with the device during the trial period, the EPG can be completely covered during the trial period. Any adjustment or suspension of EPG operation by the patient during the trial period can be made by the patient remote. 
     While the above described embodiments depict examples of patient coupling features and EPG mounting features, it is appreciated that such features could be modified to accommodate EPGs of varying sizes and shapes and still retain the use and advantages of such features as described herein. For example, affixation devices having an EPG mounting portion could include only the two retention tabs or could include four retention tabs to provide varying levels of support and retention as needed for a particular EPG configuration. In other embodiments, the multiple tabs could dimensioned and arranged to engage the EPG at various other locations depending on the size and shape of the EPG device. 
     In another aspect, trial system  100  can include differing connector cable sets for use with EPG  40  having a multi-purpose connector receptacle, such as that shown in  FIG. 12A . It is appreciated that these cables could also be used with various other EPG devices, such as EPG  50 , by use of an adapter or lead extension cable. These differing connector cable sets can include any of those depicted in the examples shown in  FIGS. 12B-12F , or various other configuration as desired. 
       FIG. 12B  depicts a lead extension  22 , which includes a proximal lead connector  24  similar or identical to that on the implantable neurostimulation lead  20  and an implantable lead connector receptacle  21 , which can be connected to a proximal lead connector  24  of a fully implanted neurostimulation lead  20 . Such a lead extension can be useful as it allows a neurostimulation lead of a length suitable for permanent implantation to be used during the trial period and remain implanted if converted to a permanent neurostimulation system. 
       FIG. 12C  depicts a grounded neurostimulation therapy cable set  26 , which includes a proximal lead connector  24  and boot  25  that is connected in parallel to an external connector receptacle  26   a  and a ground connector  26   b , which can be coupled to a ground pad applied to the patient&#39;s skin. Ground connector  26  can be an alligator or J-clip that can be attached to an adhesive ground pad, while the external connector receptacle  26   a  can be attached to a neurostimulation device  20 ′ having one or more neurostimulation leads. 
       FIG. 12D  depicts a dual neurostimulation lead cable set  27 , which includes a proximal lead connector  24  and boot  25  that is connected in parallel to two neurostimulation lead proximal connectors  27   a ,  27   b , which can be identical or different. For example, each electrical contact of the lead connector receptacle  24  can be electrically connected to a corresponding contact within the lead connectors  27   a ,  27   b  such that two identical neurostimulation leads can be coupled thereto and receive parallel stimulations along corresponding neurostimulation electrodes or be used as a bipolar pair. In other embodiments, the proximal lead connectors  27   a ,  27   b  can be configured differently, for example, each electrical contact within lead connector  27   a ,  27   b  can be electrically connected to a dedicated electrical contact within connector receptacle  24  such that two leads  20 ′,  20 ″ can simultaneously deliver differing neurostimulation stimulations. It is further appreciated that such a cable set could be modified for connection of additional neurostimulation leads or devices (e.g. three or more leads). 
       FIG. 12E  depicts a charging cable set  28 , which includes a proximal lead connector  24  and boot  25  coupled with a charging cord, which can be connected to a power adapter and plugged directly into an external power source, such as a standard wall outlet. In some embodiments, lead connector  24  could be included as an adapter and used with the same power cord as is used to charge the CP and external charger of the IPG 
       FIG. 12F  depicts a multi-lead cable set  29 , which includes a proximal lead connector  24  and boot  25  that is connected in parallel to two neurostimulation lead proximal connectors  29   a ,  29   b , which can be identical or different. For example, each electrical contact of the lead connector receptacle  24  can be electrically connected to a corresponding contact within the lead connectors  29   a ,  29   b  such that two identical neurostimulation leads can be coupled thereto and receive parallel stimulations along corresponding neurostimulation electrodes or be used as a bipolar pair. In other embodiments, the proximal lead connectors  29   a ,  29   b  can be configured differently, for example, each electrical contact within lead connector  29   a ,  29   b  can be electrically connected to a dedicated electrical contact within connector receptacle  24  such that two leads  20 ′,  20 ″ can simultaneously deliver differing neurostimulation stimulations. It is further appreciated that such a cable set could be modified for connection of additional neurostimulation leads or devices (e.g. three or more leads). Ground connector  29   c  is configured to couple with a ground pad affixed externally on the patient. 
       FIG. 13  illustrates an alternative percutaneous extension cable  22 ′ electrically connecting a multi-pin receptacle connector  25 ′ to a proximal lead connector  21 , which can be connected to a proximal lead connector  24  of a trial neurostimulation lead or a fully implanted neurostimulation lead  20 . Multi-pin receptacle connector  25 ′ is configured to connect with a multi-pin plug connector, for example lead connector  53  of EPG  50 . This cable set is particularly useful for use in an advanced trial (e.g. with a tined lead) in which the lead connector  21  is implanted and the tined lead remains implanted when the trial system is converted to a permanently implanted system. 
       FIG. 14  illustrates an alternative multi-lead cable set  29 ′, which includes a multi-pin receptacle connector  25 ′ that is connected in parallel to two neurostimulation lead proximal connectors  29   a ,  29   b , which can be identical or different. Multi-pin receptacle connector  25 ′ is configured to connect with a multi-pin plug connector, for example lead connector  53  of EPG  50 . It is appreciated that multiple leads can be electrically connected to the multi-pin receptacle connector  25 ′ according to various configurations. For example, each electrical contact of the lead connector  25 ′ can be electrically connected to a corresponding contact within the lead connectors  29   a ,  29   b  such that two identical neurostimulation leads can be coupled thereto and receive parallel stimulations along corresponding neurostimulation electrodes or be used as a bipolar pair. In other embodiments, the proximal lead connectors  29   a ,  29   b  can be configured differently, for example, each electrical contact within lead connector  29   a ,  29   b  can be electrically connected to a dedicated electrical contact within lead connector  25 ′ such that two leads  20 ′,  20 ″ can simultaneously deliver differing neurostimulation stimulations. It is further appreciated that such a cable set could be modified for connection of additional neurostimulation leads or devices (e.g. three or more leads). Ground connector  29   c  is configured to couple with a ground pad affixed externally on the patient. This connector set is more suited for a basic trial, such as a PNE trial. 
       FIG. 15  illustrates a schematic of a trial system  100 , in accordance with aspect of the invention, and a permanent system  200 . As can be seen, each of the trial and permanent system are compatible for use with a wireless clinician programmer and a patient remote. The communication unit by which EPG wirelessly communicates with the clinician programmer and patient remote can utilize MedRadio or Bluetooth capability, which can provide a communication range of about two meters. The clinician programmer can be used in lead placement, programming and stimulation control in each of the trial and permanent systems. In addition, each allows the patient to control stimulation or monitor battery status with the patient remote. This configuration is advantageous as it allows for an almost seamless transition between the trial system and the permanent system. From the patient&#39;s viewpoint, the systems will operate in the same manner and be controlled in the same manner, such that the patient&#39;s subjective experience in using the trial system more closely matches what would be experienced in using the permanently implanted system. Thus, this configuration reduces any uncertainties the patient may have as to how the system will operate and be controlled such that the patient will be more likely to convert a trial system to a permanent system. 
       FIGS. 16-17  illustrate methods of controlling operation of an EPG having a multi-purpose port in accordance with aspects of the invention. The method of  FIG. 16  includes steps of: receiving a proximal lead connector of a neurostimulation lead in a first connector receptacle of an EPG; delivering neurostimulation therapy to one or more neurostimulation electrodes of the lead with the EPG; receiving a power connector in the first connector receptacle of the EPG; and charging a rechargeable battery of the EPG with power received via the first connector receptacle. The method of  FIG. 17  includes steps of: receiving connector in a first connector receptacle of an EPG; switching to a first operating mode corresponding to a first type of connector received based on a detected characteristic of the first connector or associated electrical connection; controlling the EPG according to the first operating mode while connected to the first connector; optionally, suspending operation in the first mode upon detecting disconnection of the first connector; and switching to a second operating mode corresponding to a second type of connector received based on a detected characteristic of the second connector or associated electrical connection. Such operating modes can include but are not limited to a therapy mode corresponding to a proximal lead connector of a trial neurostimulation lead and a charging mode corresponding to a power connector coupled with a power source. It is appreciated that such methods can further include various other types of operating modes that correspond to various other types of connectors and connections as desired. 
     It is appreciated that other embodiments of the affixation device could include similar releasable mounting feature on a support substrate that allows the EPG to be readily detached by the patient. For example, the mounting features described above could be incorporated into a belt worn, a holster worn around a mid-section of the patient, or worn around the neck similar to a neck badge. 
     In the foregoing specification, the invention is described with reference to specific embodiments thereof, but those skilled in the art will recognize that the invention is not limited thereto. Various features and aspects of the above-described invention can be used individually or jointly. Further, the invention can be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. The specification and drawings are, accordingly, to be regarded as illustrative rather than restrictive. It will be recognized that the terms “comprising,” “including,” and “having,” as used herein, are specifically intended to be read as open-ended terms of art.