Peripheral Nerve Stimulation for Shoulder Pain: Dose Response

Hemiplegic shoulder pain (HSP) affects up to 60% of moderate to severely impaired stroke survivors. HSP is associated with poor rehabilitation outcomes, including interference with activities of daily living (ADLs) and poor quality of life (QoL). While many treatments for HSP have been proposed, most do not result in long-term relief of pain. The investigators developed the use of intramuscular peripheral nerve stimulation (PNS) for the treatment of HSP, which involves the temporary placement of a percutaneous intramuscular electrode to stimulate the axillary nerve motor points to the deltoid muscle. The deltoid muscle is stimulated for 6 hours per day for 3 weeks, causing comfortable, non-fatiguing contractions. This treatment, which occurs in the community setting, results in pain relief for up to 12 months when compared to treatment with a hemisling. A systematic review of randomized controlled trials (RCT) with pain as the primary outcome concluded that intramuscular PNS was the only treatment to provide long-term relief of pain for those with HSP. We have completed two RCTs that have demonstrated that a short-term PNS treatment (i.e., 3 or 6 weeks) provides pain relief. The first trial demonstrated efficacy in long-term pain relief in more than 60% of subjects for greater than 12 months. The second trial corroborated the finding that more than 60% of subjects receiving PNS achieved long-term pain reduction, and also showed that PNS reduces pain more than that achieved with physical therapy. The mechanism of action of PNS in reduction of HSP is not yet known. Thus, the primary objective of this RCT is explore the mechanism for HSP reduction. The mechanisms behind PNS for the treatment of HSP are not known. First, individual variation may contribute to response to PNS, thus we will explore the association of subject-specific clinical and demographic information and pain relief from PNS. Secondly, our team and others have found that in the chronic stage central sensitization mechanisms may also have a role in perpetuating pain, as it does in other forms of chronic shoulder pain. These mechanisms will be explored via measures of sensory and pain perception. Finally, our approach to delivering PNS for HSP is different from other treatments in which PNS is delivered through skin surface electrodes (e.g., transcutaneous electrical nerve stimulation or TENS) in that our treatment produces repeated muscle contraction over the course of weeks. Treatments such as TENS generates tingling sensations (paresthesias) over the painful area, and pain relief following stimulation is short-lived, seldom lasting more than a few hours. We postulate that long-term pain relief for HSP after PNS treatment is due to the repeated muscle contraction that occurs daily over the course of treatment, thus we will explore the dose-response association of muscle-contraction from PNS and pain reduction, completion of activities of daily living (ADLs), and improvement in quality of life.