The effect of High-Definition Transcranial Direct Stimulation (HD-tDCS) on pain in Somatic Symptom Disorder with predominant pain (SSD-P): a randomized single-blind sham controlled cross- over study

AIM: Somatic Symptom Disorder with predominant pain (SSD-P) is a common disorder with unsatisfactory treatment options. Non-invasive brain stimulation such as tDCS is useful in various chronic painful conditions. The aim of the study was to assess the effect and safety of 2 sessions of HD-tDCS over left motor cortex on pain and other associated variables in SSD-P on appropriate rating scales. METHODOLOGY: Institute Ethics Committee approval was sought and registered in the Clinical Trials Registry of India. Single-blind, sham controlled, cross-over study design was employed. Thirty right handed patients with DSM-5 diagnosis of SSD-P, aged 18-60 years, receiving stable treatment were enrolled by consecutive sampling. After block randomization, a novel protocol (2 short interval repeated sessions) of either active or sham HD-tDCS was administered followed by a wash out period of 7 days and cross over. Assessments were done at baseline, week 1 and 2. RESULTS: Participants were comparable on all baseline parameters. ANCOVA showed no order×group interaction. On RM-ANOVA all participants irrespective of entering active or sham arm showed statistically significant difference (with good effect size, Cohen’s d >0.8) in pain and associated parameters like depression, anxiety, pain related interference, burden and disability at week 2. But at week 1, this was observed only in active arm. Transient mild local side effects like burning, pain and itching were noted. No cognitive side effects were observed. DISCUSSION: This was the first study of HD-tDCS on SSD-P. Bias due to randomization, order of stimulation and blinding was ruled out. Single session repeated protocol can be effective in pain reduction and other parameters. Effects were sustained over a week. CONCLUSION: 2 sessions of active HD-tDCS is safe and effective in reduction of pain and other associated variables like interference, burden and disability in SSD-P. Trial of short protocols is further required.