Background: Myofascial pain syndrome (MPS) in the shoulder is among the most prevalent pain problems in the middle-aged population worldwide. Evidence suggests that peripheral and central sensitization may play an important role in the development and maintenance of shoulder MPS. Given previous research supporting the potential efficacy of anodal transcranial direct current stimulation (tDCS) for modulating pain-related brain activity in individuals with refractory central pain, we hypothesized that anodal tDCS when applied over the primary motor cortex (M1) combined with standard treatment will be more effective for reducing pain in patients with MPS than standard treatment alone.
Methods and materials: Study participants were randomized to receive either (1) standard treatment with 5 consecutive days of 1 mA anodal tDCS over M1 for 20 minutes; or (2) standard treatment plus sham tDCS. Measures of pain intensity, shoulder passive range of motion (PROM), analgesic medication use, and self-reported physical functioning were administered before treatment and again at posttreatment and 1-, 2-, 3-, and 4-week follow-up.
Results: Thirty-one patients with MPS were enrolled. Participants assigned to the active tDCS condition reported significantly more pretreatment to posttreatment reductions in pain intensity that were maintained at 1-week posttreatment, and significant improvement in shoulder adduction PROM at 1-week follow-up than participants assigned to the sham tDCS condition.
Conclusions: Five consecutive days of anodal tDCS over M1 combined with standard treatment appears to reduce pain intensity and may improve PROM, faster than standard treatment alone. Further tests on the efficacy and duration of effects of tDCS in the treatment of MPS are warranted.