Somatic symptom disorder with predominant pain (SSD-P) is a commonly encountered disorder, yet treatment options often yield unsatisfactory outcomes. Transcranial direct current stimulation (tDCS) has proven useful in chronic pain conditions and may hold potential for treating somatoform pain. High-definition tDCS (HD-tDCS) offers more precise cortical stimulation than conventional tDCS. However, this modality has not been extensively studied in SSD-P. Consequently, this study aims to assess the effects of a novel HD-tDCS protocol on pain and other associated variables in patients with SSD-P. The Institute Ethics Committee approved the study, which was also registered in the Clinical Trials Registry of India. A single-blind, sham-controlled, crossover study design was employed. Thirty right-handed patients with DSM-5 diagnosis of SSD-P, aged 18 – 60 years and receiving stable treatment, were enrolled through consecutive sampling. After simple randomization, two repeated, short-interval sessions (2 mA, 20 min each) of either active or sham HD-tDCS were administered, followed by a washout period of 7 days and a subsequent crossover. Assessments were conducted at baseline, week 1, and week 2. Participants in active and sham arms were comparable on all baseline parameters. At the end of the 1st week, patients in the active group showed significant improvement in the study variables compared to the sham group. By week 2, all participants, irrespective of being in the active or sham arm, demonstrated a statistically significant difference (Cohen’s d > 0.8) in pain and associated parameters such as depression, anxiety, pain-related interference, burden, and disability (P < 0.01). Transient mild local side effects such as burning, pain, and itching were noted, with no cognitive side effects reported. In conclusion, this novel HD-tDCS protocol is effective in reducing pain in patients with SSD-P, with sustained effects up to 1 week.
