Intrathecal Morphine Microdose Method Sensory Changes

Following the retrospective study on the effectiveness of the microdose method of intrathecal morphine therapy, the investigators are interested in measuring the sensory changes at 4 time points during the microdose method. The microdose method involves weaning the patient off oral opioids and maintaining an opioid-free period prior to initiating a very low opioid dose in intrathecal therapy. The microdose method is a standard of care. The study involves measuring sensory changes to hot, cold, and pressure. Data collection will be performed at regularly scheduled clinic visits, examining range of doses, pain scores,dose escalations, quantifiable psychosocial factors ( not captured in previous retrospective study), and changes in sensory thresholds.

The use of intrathecal drug delivery systems for the management of chronic non-cancer pain has been in practice for over 30 years. A recently published study from the University of Texas Medical Branch performed a retrospective review on the morphine microdose method in community-based clinics. The goal of the study was to examine the morphine microdose method in an outpatient setting and assess success of therapy, pain scores and dose escalation. Patients were successfully weaned off their systemic opioids, maintained in an opioid-free period for 4-6 weeks, and then underwent a microdose trial and implantation. The majority of patients were successfully managed on morphine monotherapy, with a significant reduction in pain scores, and dose escalations comparable to prior studies. No prospective studies have examined the microdose method in correlation with changes in pain sensitivity.

Several studies have looked at the use of various pain testing models to investigate the effects of chronic opioid therapy and changes in pain perception. A systematic review of the literature identified clinical studies incorporating measures of hyperalgesia in patients on chronic opioid therapy. This review was aimed at finding the optimal testing modality to evaluate pain threshold and tolerance to external stimuli, including mechanical (pressure, touch, injection), thermal (cold/heat), and electrical. Although the results did not reveal any one method with sufficient power, several prospective studies evaluating hyperalgesia with heat pain ratings have shown some promising results; two studies revealing significant changes in heat responses for opioid treatment groups, and one study demonstrating lower heat pain perception values following an opioid taper. The latter study of research pertaining to pain sensitivity changes following an opioid taper is lacking, and only recently was a study performed investigating changes in pressure threshold following transition from full mu agonist to buprenorphine. Little is known at this juncture how pain thresholds change due to opioid dose changes and/or route of delivery changes such as oral to intrathecal routes.

Eligibility Criteria:
Inclusion Criteria:

* Age between 18 and 75
* Selected for microdose Intrathecal pump therapy by their pain physician
* Chronic pain for at least 3 months
* Willing to cooperate with all study procedures

Exclusion Criteria:

* Presence of cancer
* Age less than 18 years old or greater than 75
* Current intrathecal therapy and/or with multiple intrathecal drugs (such as other opioids, local anesthetics, muscle relaxants)
* Medical conditions (myocardial infarction within the last year, uncontrolled diabetes, autoimmune disease
* Recent history of alcohol or substance abuse in the last 5 years