Are obsessive-compulsive symptoms expression of vulnerability to bipolar disorder?

Abstract

More than half of patients with bipolar disorder (BD) have anadditional diagnosis, one of the most difficult to manage beingobsessive–compulsive disorder (OCD). French psychiatristB!en !edict Augustin Morel first described patients with BD-OCD arising questions around the nosological and clinicalmeaning of this condition. In a standard 1969 psychiatrytextbook, Mayer-Gross and colleagues, mostly consideringcourse of illness, included patients with BD-OCD in themanic-depressive disorders (1). Although recent studies haveinvestigated the co-occurrence of anxiety and bipolar disor-ders, the topic is insufficiently studied and the relationshipbetween BD and OCD remains unclear. However, given theavailable scientific evidence, some observations can be made.i) Apparent BD-OCD comorbidity is a common conditionin psychiatry. In our recent meta-analysis, the pooledprevalence of OCD in BD was 17.0% (95% CI 12.7–22.4%), which was comparable to the results reported bythe pooled prevalence of BD in OCD (18.35%, 95% CI13.2–24.8%) (2). Although limited by retrospective studydesign, small sample size, different thresholds for BDdiagnosis (i.e. categorical vs. dimensional approach) anda different accuracy in diagnosing OCD (i.e. discrimina-tion between true ego-dystonic obsessions and depressiveruminations), these results confirm the relevance ofcomorbid BD-OCD.ii) As reported by recent studies, OC symptoms in childhoodand adolescence increase the risk of a later BD diagnosis(3). These results would be suggestive of partially sharedaetiopathogenetic mechanisms between these severe men-tal disorders.iii) In our previous systematic review, considering course ofillness as a key diagnostic validator, especially amongpatients with a primary diagnosis of BD, the majority ofcomorbid OCD cases appeared to be related to mood epi-sodes (1). OC symptoms in comorbid patients appearedmore often – and sometimes exclusively – during depres-sive episodes, and comorbid BD and OCD cycledtogether, with OC symptoms often remitting duringmanic/hypomanic episodes.iv) Results from our meta-analysis showed higher comorbid-ity rates in youths (24.2%, 95% CI = 10.36–41.60,n = 345, z = !9.5) compared to adults (13.56%, 95%CI = 10.4–16.25, n = 4,539) (2). In other words, OCsymptoms would initially coexist with BD symptoms andthey would gradually tend to decrease in the adulthood.v) From a neurobiological perspective, BD mostly showedhypoactivity in orbitofrontal cortex (OFC) (i.e. decisionmaking, impulse control) and in dorsolateral prefrontalcortex (DLPFC) (i.e. planning, attentional set shifting)with grey matter volume reduction associated to manicepisodes, while OCD mainly presented hyperactivity ofOFC with deficit in emotional processing (4). The overlapof similar cortical–subcortical circuits may partiallyexplain clinical features of comorbid patients with BD-OCD during the course of illness.vi) The clinical features of comorbid patients with BD-OCD would explain why OCD and BD symptomsrespond to adequate mood stabilizer treatment (5).Only in a minority of comorbid patients with persis-tent OCD, despite improvement in mood episodes,addition of low doses of antidepressants could be con-sidered while strictly monitoring emerging symptomsof mania or mixed states.To conclude, according to the available literature, we specu-late that OC symptoms in childhood and adolescence may beexpression of vulnerability to BD increasing the risk of a laterBD diagnosis. OC symptoms would initially coexist with BDsymptoms even cycling together, and they would graduallytend to decrease in the adulthood.Considering the important nosological, clinical and thera-peutic implications, further original studies are needed to clar-ify BD-OCD comorbidity. In particular, studies addressingneurobiological substrates are essential to illuminate patho-genetic mechanisms that underlie comorbid BD-OCD.