Obsessive compulsive disorder (OCD) is an anxiety syndrome marked by intrusive and aversive thoughts that are accompanied by repetitive actions or rituals. The symptoms of OCD are distributed continuously on a spectrum from mild to severe [1
], and approximately 2% of the population meets diagnostic criteria [2
]. OCD is associated with a wide range of psychosocial and occupational impairments and is often extremely distressing to the individuals and their families [4
]. Along with a marked heterogeneous symptom profile, substantial comorbidity represents a hallmark feature of OCD. The presence of additional comorbid disorders has been associated with further impairment in functioning [5
], greater OCD symptom severity [6
], and lower treatment response [7
]. Comorbidity with specific disorders also raises important etiological and classification questions [9
]. By definitively documenting different comorbidity patterns, researchers can begin to investigate the underlying causes of co-occurrence and subsequently refine the conceptualization of the psychopathology in question [10
]. In addition, clarifying comorbidity patterns will allow researchers to examine constellations of common traits, which may, in turn, lead to the identification of common etiological factors [11
]. This is particularly germane for detecting clusters of genes that may contribute to comorbid disorders.
Patients with OCD experience elevated comorbidity levels over a wide range of affective, anxiety, and other Axis I disorders, as compared to the general population [12
]. In fact, only a small proportion of individuals with OCD, approximately 8%, do not appear to have any comorbid disorders [13
]. Considering specifically the affective disorders, one would expect—based on chance alone—relatively low rates of comorbidity: with major depressive disorder (MDD) in only .3% of cases and with bipolar disorder (BPD) in only .04% of cases. In reality the rates are much higher—across the different diagnostic categories, affective syndromes stand out as the most commonly comorbid in samples of OCD. Lifetime major depressive disorder (MDD) affects between 41% and 70% of individuals with OCD [6
], as compared to 17% of the general population [17
]. Bipolar disorder (BPD), which is prevalent in 1.6% of the general population, is also commonly comorbid and affects a reported range of 1–23% of clinical OCD samples [6
]. The large discrepancy between what would be true based on chance and the actual co-occurrence of these disorders points to the need to further understand the intricate relationships between OCD and the mood disorders.
The most commonly comorbid disorder with OCD is MDD [6
], and it has been noted that the two disorders share certain phenomenological features in common, including frequent agitation, indecision, guilt, and other cognitive factors [18
]. Although both MDD and OCD respond to similar antidepressants [7
], a diagnosis of comorbid MDD with OCD contributes significantly to increased severity of illness [20
] and greater rates of additional comorbidity [21
]. OCD patients with comorbid MDD have been found to endorse an earlier age of onset of OCD [21
], and a recent OCD family study found support for elevated levels of familiality for depressive disorders [22
]—two factors that might underlie a genetic predisposition for MDD and OCD.
The potential link between BPD and OCD is also noteworthy. A recent epidemiological investigation of the 12-month prevalence of obsessive compulsive symptoms in Germany found that a diagnosis of OCD was associated with significantly increased chances (OR = 22.6) of also being diagnosed with probable BPD [23
]. Likewise, rates of OCD in samples of BPD reveal high comorbidity ranging from 7–21% [24
]. Past research on OCD-BPD comorbidity has illustrated that patients with OCD and BPD are at elevated risk for high levels of comorbidity with other disorders, including generalized anxiety disorder, social phobia, panic disorder, agoraphobia, and alcohol and substance use disorders [27
]. From the clinical perspective, there is also an acknowledgement that individuals with OCD and BPD are among the most treatment resistant. Collectively, there is suggestive evidence that patients with OCD-BPD represent a unique group in terms of symptom presentation and impairment [32
], and examining this comorbidity may help to elucidate a psychopathological link between the two disorders.
The current report attempts to further clarify the role that affective disorder comorbidity—particularly that with BPD—may play in the clinical expression of OCD. Our primary aim was to consider the clinical impact of affective disorder comorbidity on the phenomenology and clinical features of OCD. A previous investigation by Perugi and colleagues [29
] conducted a similar analysis; however, the current report sought to extend that examination by addressing a number of sampling and methodological limitations. In addition to relying on a substantially larger N, our investigation examined a non-treatment seeking OCD population and contrasted three OCD participant groups: (1) those with BPD, (2) those with DD, (3) and those with no affective disorder comorbidity. Factors considered included demographic and treatment variables, comorbidity patterns, measures of impairment and functioning, and clinical features of OCD. Importantly, we controlled for overall (non-mood disorder) comorbidity levels in our group comparisons on impairment and the clinical features of OCD. We hypothesized that BPD group status would be associated with the greatest levels of severity, and that the DD group would be more severe than the NAD group.