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.

Inclusion Criteria:

- shoulder pain localized to the glenohumeral joint, subacromial area or deltoid
insertion associated with: a) rest; b) passive abduction or external rotation range of
motion (ROM); c) active abduction ROM; or, d) manual palpation;

- shoulder pain onset or worsening after the most recent stroke;

- weakness of shoulder abductors (≤4/5 on MRC if isolated movement is present);

- ≥ 21-yrs old; < 90-yrs old;

- time of stroke ≥ 3-mo;

- duration of HSP ≥3-mo;

- HSP with moderate to severe pain (BPI SF-3 ≥ 4);

- cognitive and communication ability to fulfill study requirements (cognitive ability
based upon a score of ≥24 on the Mini Mental Status Exam (MMSE));

- availability of reliable adult who can assist with study procedures if necessary;

- willing and able to report shoulder pain and other conditions and complete study
visits throughout the 4 month study period.

Exclusion Criteria:

- joint or overlying skin infection or history of recurrent skin infections;

- insensate skin;

- need to take > 1 opioid and > 1 nonopioid analgesic medication for HSP;

- regular intake of pain medications for another chronic pain;

- botox injection or subacromial steroid injections to the shoulder within the past 12
wks;

- receiving OT or PT for HSP;

- bleeding disorder or INR > 3.0;

- sensitivity to skin surface electrodes and/or medical-grade adhesives, gels, tapes;

- medical instability;

- pregnancy;

- uncontrolled seizures (>1/mo for 6-mo);

- history of cardiac arrhythmia with hemodynamic instability;

- history of lidocaine allergy;

- history of Parkinson's disease, SCI, TBI, MS, or ipsilateral UE lower motor neuron
lesion;

- history of complex regional pain syndrome, myofacial pain syndrome, other pain
conditions (investigator discretion);

- cardiac pacemaker or other implanted electronic device;

- history of valvular heart disease (artificial valves, requiring antibiotics for
procedures, etc.);

- severely impaired communication.