Significant proportion of patients with obsessive compulsive disorder (OCD) continues to be disabled due to inadequate treatment response despite adequate treatment with selective serotonin reuptake inhibitors (SSRIs). The treatment options in such situations are limited and there is a need to evaluate more “neurobiologically informed” treatment approaches in OCD. Earlier studies have reported potential utility of add-on conventional transcranial Direct Current Stimulation (tDCS) in treatment-resistant OCD. Conventional tDCS modulates cortical regions wider than intended. Additionally, the largest cortical current density might not be localised directly beneath the target electrode. These factors may contribute to the inconsistent observations on the effect of add-on tDCS for OCD. High-Definition tDCS (HD-tDCS) is a recent advancement of technique which optimizes the neuromodulation through focalized current application.

In this report, we describe the first-time application of add-on HD-tDCS in SSRI-resistant OCD patients. Pre-Supplementary Motor Area (Pre-SMA) the target chosen for anodal stimulation considering its important role in the neurobiological understanding of the disorder.

Fourteen patients [Age=35.9±8.4years; male:female=11:3]with DSM-V-OCD having persistent symptoms despite adequate and stable treatment with SSRIs were administered HD-tDCS (anodal 2mA, right Pre-SMA). Two sessions of 20minutes each per day, scheduled 20minutes apart were administered for 5 consecutive days. HD-tDCS was administered using standard equipment (Soterix Medical MxN HD system; mxn.php) using stringent safety measures. The MxN HD-tDCS system offers a technical enhancement with optimised electrodes and montage configurations that substantially increase the focality of stimulation. The target of stimulation was ascertained using neuronavigation done after acquiring T1 weighted MRI. Those patients achieving at least 25% reduction in YBOCS total score were categorized as “responders”. At the end of each session, a structured questionnaire was used to assess any potential adverse effect that might have occurred either during or after the HD-tDCS session.

There was a significant reduction in YBOCS total score after HD-tDCS sessions [Baseline vs. Post HD-tDCS=27.6±5.7 vs. 19.4±8.0, t=3.9, P=0.002]. Mean percentage reduction in YBOCS total score was 29.1±23.6 (median=25.8) and there were 8 (57.1%) responders. There were no significant adverse effects reported by the patients.

To the best of our knowledge, this is the first study in OCD examining the feasibility and clinical utility of add-on HD-tDCS over the pre-SMA in a 4×1 ring configuration to treat persistent symptoms unresponsive to the conventional pharmacotherapeutic options. In our patients, we observed rapid amelioration of distressing OCD symptoms with add-on HD-tDCS. All sessions were very well tolerated by the patients and they reported no adverse effects either during or after HD-tDCS. Overall, the results from this preliminary open-label observation of HD-tDCS in OCD shows promise for its use in this condition. HD-tDCS may evolve as a treatment option for treatment resistant OCD. Future research is required in this field. Particularly, the efficacy of add-on HD-tDCS in OCD required rigorous evaluation using a randomised, sham-controlled design.