Identifying trajectories of symptom change in adults with obsessive compulsive disorder receiving exposure and response prevention therapy.

Exposure and response prevention (EX/RP) is a recommended psychotherapy for obsessive-compulsive disorder (OCD). Yet, not all patients benefit equally from EX/RP. Prior studies have examined EX/RP predictors by predicting endpoint symptoms and/or pre-post symptom change, rather than accounting for trajectories of symptom change across treatment. We pooled data from four NIMH-funded clinical trials, yielding a large sample (N = 334) of adults who received a standard course of manualized EX/RP. Independent evaluators rated OCD severity using the Yale-Brown Obsessive-Compulsive Scale (YBOCS). Data were analyzed using growth mixture modeling (GMM) to detect subgroups of participants with similar trajectories of symptom change followed by multinomial logistic regression to identify baseline variables capable of predicting class membership. GMM revealed three distinct trajectory classes: 22.5% of the sample showed dramatic improvement (dramatic progress class), 52.1% showed moderate improvement (moderate progress class), and 25.4% showed little change (little to no progress class). Membership in the little to no progress class was predicted by baseline avoidance and transdiagnostic internalizing factor levels. These findings suggest that OCD symptom improvement with outpatient EX/RP occurs via distinct trajectories. These findings have implication regarding identifying treatment non-responders and personalizing treatment depending one's baseline characteristics in order to optimize treatment effectiveness.