The Role of Transcranial Direct Current Stimulation in Chronic Shoulder Pain: A Scoping Review

Background: Chronic shoulder pain is a prevalent musculoskeletal disorder often associated with central sensitisation, which limits the effectiveness of conventional therapies. Transcranial direct current stimulation (tDCS) has emerged as a non-invasive neuromodulatory intervention to modulate cortical excitability and potentially improve pain and functional outcomes. Methods: This scoping review followed the Joanna Briggs Institute (JBI) framework and PRISMA-ScR guidelines. A systematic search was conducted across MEDLINE, CENTRAL, Scopus, PEDro, and Web of Science to identify studies evaluating the effects of tDCS on pain and function in adults with rotator cuff disorders, myofascial pain syndrome (MPS), or subacromial pain syndrome (SAPS). Data were extracted and synthesised qualitatively. Results: Four studies met the inclusion criteria. tDCS demonstrated variable efficacy: some trials reported no additional benefit when used alongside corticosteroid injections or sensorimotor training (e.g., SAPS and rotator cuff tendinopathy), while others showed enhanced pain reduction and functional gains, particularly in MPS. Targeting the dorsolateral prefrontal cortex (DLPFC) appeared more effective than stimulating the primary motor cortex (M1) in modulating pain. Functional improvements were generally observed, though not consistently superior to sham interventions. Conclusions: Preliminary evidence suggests that tDCS may represent a promising adjunctive treatment for chronic shoulder pain, particularly in MPS. However, due to the limited number of studies and heterogeneity in methods, conclusions should be interpreted with caution. However, heterogeneity in study protocols, stimulation targets, and patient populations limits conclusive recommendations. Standardised protocols and larger trials are needed to determine the optimal application of tDCS in clinical shoulder pain management.