Identifying patients with obsessive-compulsive disorder using whole-brain anatomy.

Structural neuroimaging studies have reported a variety of brain alterations between groups of obsessive-compulsive disorder (OCD) patients and healthy controls. However, the large heterogeneity in discrete anatomical measures that exists among patients prevents a clear discrimination of single patients from healthy subjects. This reduces the potential clinical applicability of structural neuroimaging studies. In the present study we assessed the feasibility of identifying OCD patients on the basis of whole-brain anatomical alterations. Whole-brain magnetic resonance images were collected from two consecutive samples of OCD outpatients (n=72 and n=30), and control subjects (n=72 and n=30). We computed the whole-brain (voxel-wise) pattern of structural difference between OCD patients and control subjects at the group level. A single expression value of this difference pattern was calculated for each subject, expressing their degree of 'OCD-like' anatomical alteration. Accuracy of patient classification based on these expression values was assessed using two validation approaches. Firstly, using a cross-validation method, we obtained a high classification accuracy (average of the sensitivity and specificity indices) of 93.1%. In a second assessment, which classified new groups of OCD patients and control subjects, overall accuracy was lower at 76.6%. Individual expression values for OCD patients were significantly correlated with overall symptom severity as measured by the Y-BOCS scale. Our results suggest that OCD patients can be identified on the basis of whole-brain structural alterations, although the accuracy of our approach may be limited by the inherent variability of psychiatric populations. Nevertheless, the anatomical characterization of individual patients may ultimately provide the psychiatrist with relevant biological information.