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

BackgroundSomatic Symptom Disorder with predominant pain (SSD-P) is a common disorder with unsatisfactory treatment options. Transcranial Direct Current Stimulation (tDCS) is useful in chronic pain conditions. ObjectiveTo assess the effect of two within session repeated High Definition tDCS (HD-tDCS) over left motor cortex on pain and other associated variables in SSD-P. MethodsInstitute Ethics Committee approval was sought and the study was 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 simple randomization, two short interval repeated sessions (2mA, 20 minutes each) of either active or sham HD-tDCS was administered followed by a wash out period of seven days and cross over. Assessments were done at baseline, week one and two. Analysis was done using SPSS 21. ResultsParticipants were comparable on all baseline parameters. ANCOVA showed no orderxgroup interaction. On RM-ANOVA all participants irrespective of entering active or sham arm showed statistically significant difference (Cohens d >0.8) in pain and associated parameters like depression, anxiety, pain related interference, burden and disability at week two (p< 0.01). But at week one, this was observed only in active arm. Transient mild local side effects like burning, pain and itching were noted, with no cognitive side effects. ConclusionThis was the first study of HD-tDCS on SSD-P. Single session repeated protocol can be effective in pain reduction with sustained effects up to one week.