Comparison of Constant Current to Constant Voltage Stimulation in Subthalamic Deep Brain Stimulation for Parkinson's Disease
Condition: Parkinson's Disease
MeSH terms: Parkinson Disease
Study type: Interventional

Summary: 
      HYPOTHESIS: Constant current stimulation for STN DBS will allow better and more stable
      control of Parkinson's disease symptoms than constant voltage stimulation.

      Subthalamic nucleus (STN) deep brain stimulation (DBS) is an established therapy for advanced
      Parkinson's disease (PD). Two types of implantable pulse generators (IPGs) are available,
      differing on whether voltage or electrical current is controlled. Constant current IPGs
      provide a specific electrical current and will automatically adjust the voltage depending on
      the impedance, while the current applied by constant voltage IPGs will depend on the tissue
      impedance that may change over time. No study has compared the clinical differences of these
      two electronic modalities.
    

Detailed description: 
      Deep brain stimulation (DBS) is an established therapy for neurological and psychiatric
      disorders, being one of the most important therapies in functional neurosurgery to date.
      Class I evidence shows that subthalamic nucleus stimulation (STN) for Parkinson's disease
      (PD) is more effective than the best medical therapy (1,2). Globus pallidus internus
      stimulation for primary dystonia has an improvement rate of up to 70%(4) and is considered
      the main surgical treatment for this pathology. Symptom improvement in essential tremor is
      well documented. Pain, epilepsy, psychiatric disorders such as Tourette syndrome, obsessive -
      compulsive disorder and depression are promising applications of DBS. Obesity, memory
      improvement, aggressiveness, drug addiction, minimal conscious state and hypertension are
      areas of continuing investigation as potential applications of DBS.

      The clinical effects of DBS result from the delivery of electrical charge to brain tissue.
      The way this electrical charge is delivered depends on the electronics of implantable pulse
      generators (IPGs). IPGs apply pulses of electrical stimulation in which voltage or current
      increases from zero to a maximum value for a period of time (order of tens of microseconds)
      and then returns to zero.

      There are two types IPGs , differing on whether voltage or electrical current is controlled
      (3).

        1. Constant - voltage IPGs: in this type of IPG there is control over the maximum voltage
           associated with each pulse. The maximum current will vary depending on the impedance. A
           specific voltage is programmed. The amount of electrical current delivered with a
           constant voltage depends on the impedance of the tissue and the electrodes. Thus, the
           voltage will not indicate how much electrical current is given; the resistance will
           determine this parameter.

        2. Constant - current IPGs: provide a specific electrical current and will automatically
           adjust the voltage depending on the impedance. The strength of stimulation will remain
           the same regardless of changes in the impedance. The difference in impedances on each
           electrode and the intersubject variability in impedances will not alter the electrical
           current by modifying the voltage.

      Until fairly recently, only constant voltage IPG's have been available for use. A newer
      generation of IPG's have been available for more than a year that can provide either constant
      voltage or constant current according to physician and patient preference. There is no
      evidence yet to support the preferential use of one modality over the other.

      IMPORTANCE OF THE STUDY Following DBS electrode implantation, the impedances within the same
      patient can vary widely. Surgical implantation changes tissue impedance, being usually higher
      immediately after surgery. In this case the patient will require higher electrical currents.
      After the initial tissue reaction subsides, the reduction of impedance will generate an
      increase of the charge density. For this reason it is commonplace to wait at least 2 weeks
      after electrode implantation before programming the IPG.

      Furthermore, different contacts on the same DBS lead can have widely varying impedances.
      Effects or side effects associated with stimulation of one electrode contact often cannot be
      applied to a different contact on the same DBS lead in the same patient because the
      impedances may differ.

      The range of impedances that can be measured will depend on the choice of voltage. In some
      patients, the voltage used therapeutically may not be enough to allow an accurate measure of
      the impedances, causing confusion regarding the structural and electrical integrity of the
      IPG.

      For all the above mentioned factors, the clinical results in patients with constant - voltage
      IPGs will depend on the experience of the operator to deal with the different aspects related
      to tissue and electrode impedances to achieve the desired current. The electronic properties
      of constant - current IPGs allows the system to make voltage adjustments in order to maintain
      the desired current and the subsequent clinical effect. This has been the theoretical
      background for the development of constant current IPG's; whether or not this theory is true
      in practice is the subject of this study.
    

Intervention name(s): Deep Brain Stimulation (Medtronic, Activa PC)
Intervention type(s): Device
Intervention description(s): Following subthalamic nucleus deep brain stimulation patients will be randomized to receive either constant current or constant voltage stimulation and subsequently "crossed over" to receive the other type of stimulation
Other intervention name(s): Medtronic; Activa PC
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Treatment
Keywords: Deep Brain Stimulation; Parkinson's Disease; Subthalamic Nucleus; Constant Current