The Efficacy of Motor Cortex Stimulation for Pain Control

This is a prospective, blinded randomized crossover study comparing two stimulation paradigms in three different groups of patients receiving motor cortex stimulation. The aim of this study is to examine the effectiveness of this modality in a controlled blinded manner, which has not been done in previous studies. There are two primary purposes of this study. The first is to compare two different stimulation paradigms: "high" level stimulation (i.e. stimulator activated 'on' for 10 minutes, 'off' for 2 hours; presumed therapeutic dose); versus "low" stimulation ('on' for 1 minute, 'off' for 6 hours; presumed subtherapeutic dose), in a prospective blinded crossover study design.

The second purpose of this study, is to examine the outcome of MCS in three different pain groups. These are:

• Unilateral upper extremity neuropathic pain such as brachial plexus avulsion, stump pain or phantom limb pain
• Neuropathic deafferentation facial pain
• Upper extremity complex regional pain syndrome (CRPS)

Measurements of the effects of motor cortex stimulation will include a visual analogue scale (VAS) of perceived pain, the McGill Pain Questionnaire, SF-36 quality of life questionnaire, Beck Depression Inventory-II, the standard 7-point patient global impression of change (PGIC), medications log (verified by pharmacy records) and an employment status questionnaire. Adverse events will be recorded at each visit.

Table 1:

Visit Study Week Standard Care 0a 1b 12c 24d 1a 2e 3f 4g F/Uh Clinic Visit X X X X X X Consent X Surgery X X X Program MCS X X X X X X VAS X X X X X X X SF-36 X X X X X X X Medications Log X X X X Employment Status X X X X McGill Pain X X X X X X X Beck Depression II X X X X Global impression of change X X

• Screening visit in consideration of MCS
• Immediate post-op visit, randomization to high or low settings
• 12 week crossover point
• Final study visit, MCS programmed at 'best' settings
• Trial period of MCS, lasting for 1 to 2 weeks
• Clinic visit to determine efficacy of MCS and removal of temporary external system.
• Permanent implantation of MCS, if trial was successful
• Follow-up as required.

Inclusion criteria

• Diagnosis in one of the following three categories:

• Unilateral upper extremity neuropathic pain such as phantom limb pain, stump pain or brachial plexus avulsion
• Neuropathic deafferentation facial pain
• Upper extremity complex regional pain syndrome (CRPS)
• Pain is refractory to conservative methods (e.g. medications, regional blocks) as reviewed by a chronic pain clinical physician
• Patient is considered a good candidate for neurosurgery, i.e. no other medical problems that would preclude surgery
• Patients who are willing to provide informed consent.

Exclusion criteria

• Patients who are not considered medically fit for neurosurgery.
• Patients who have not exhausted conservative methods of pain control, prior to considering motor cortex stimulation.
• Patients who are not able to provide informed consent.
• Patients unable to have magnetic resonance imaging (MRI).