Letter: A Systematic Review of Deep Brain Stimulation Targets for Obsessive-Compulsive Disorder

To the Editor: We read with great interest the article by Raviv and coauthors entitled “A Systematic Review of Deep Brain Stimulation Targets for Obsessive Compulsive Disorder,”1 recently published in Neurosurgery. Using a certain set of search criteria, the authors identified and elegantly discussed a total of 28 studies on deep brain stimulation (DBS) for obsessive-compulsive disorder (OCD), including 9 randomized controlled trials, 1 cohort study, 1 case-control study, 1 cross-sectional study, and 16 case series. As pointed out by Raviv et al,1 the studies included in the review suffer from many limitations that mainly concern the small sample sizes and the heterogeneity of clinical presentations, parameters for efficacy assessment, follow-up periods, and target definition. The most commonly reported targets with the highest response rates were the anterior limb of the internal capsule (ALIC), the nucleus accumbens (NAc), and the ventral capsule/ventral striatum (VC/VS). Other targets were also considered, such as inferior thalamic peduncle (ITP), globus pallidus internus (GPi), and subthalamic nucleus (STN), with promising results. The authors1 propose adopting a common nomenclature to refer to the “striatal region,” which comprises VC/VS, NAc, ALIC, and bed nucleus of stria terminalis (BNST). Indeed, the coordinates in different studies are similar, and VC/VS anatomically overlaps with ALIC and NAc, the most ventral part of the striatum below ALIC. They emphasize that VC/VS represents a region rather than a single entity and that DBS electrodes crossing different structures can simultaneously stimulate multiple targets (ALIC/NAc, ALIC/BNST, caudate/NAc) along the same axis depending on the active contacts. In this view, the authors stress the importance of applying a uniform terminology with corresponding stereotaxic coordinates, specifying the active contacts to standardize the literature on DBS for OCD. According to the authors, the outcome assessment also requires homogenization by employing scales that measure therapeutic efficacy, focusing on OCD’s various phenotypical aspects, although most studies used the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). We would like to highlight the relevance of a study by Menchón et al,2 also involving our center. This study (ClinicalTrial.gov identifier: NCT01135745), excluded by the review, represents the first prospective, open-label, interventional multicenter trial investigating the efficacy and safety of stimulation of ALIC in patients with severe treatment-resistant OCD. Concerning the targeting technique, the electrodes were located according to the surgeon's experience and the patient's anatomic features but allowing ALIC stimulation. The atlas slices included in the article summarize the location of the center of all 58 cathodes at 12 mo follow-up. A total of 30 patients were implanted, positioning active contact at the center of ventral ALIC (56%), BNST (27%), lateral hypothalamus (5%), globus pallidus externus (GPe) (2 hemispheres), and dorsal ALIC (1 hemisphere). The mean Y-BOCS score at 12 mo of follow-up decreased from baseline by 42%. Moreover, 60% of patients resulted as responders (at least 35% reduction in Y-BOCS score), one-third of which had active contact in ALIC and 33% in BNST. Furthermore, comorbid depressive symptoms, global functioning, and health level all improved in response to DBS. We agree with Raviv and coworkers1 on the importance of considering the distinct phenotypical aspects of OCD, including comorbidities, to identify the optimal personalized target for each patient. As a matter of fact, OCD is a complex and heterogeneous disease, with many different symptoms that reflect the complexity of the different brain structures involved, such as the ALIC, VC/VS, NAc, anteromedial STN, or ITP. This complexity, in part, also explains the different targets so far used. However, considering that the modulation of different targets could lead to the same results, we would suggest the promising future perspective of the “connectome approach” through tractography techniques. In movement disorders, DBS has recently experienced a paradigm shift from stimulation of specific brain nuclei to a real modulation of brain networks. In other words, different targets may modulate the same neural network responsible for the clinical improvement. Li and coauthors3 in a multicentric, international group analyzed 4 cohorts of OCD patients submitted to DBS using a connectome approach: the same results were obtained, for example, with ALIC-DBS or STN-DBS. A similar approach should explain the results reported in DBS for OCD. To summarize, the authors1 should be praised for their request for a common language in describing anatomy, localization, and target interconnections, as well as the results, when analyzing the impact and efficacy of neuromodulation for OCD. Nevertheless, we think that a paradigm shift is necessary for the future of neurosurgical treatments for psychiatric disorders, considering the modulation of the brain networks involved in the disease instead of the various targets representing the nodes of the circuits. Funding This study did not receive any funding or financial support. Disclosures The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.