The co-occurrence of obsessive-compulsive symptoms (OCS) and psychotic illness has been a challenge for clinicians and investigators for more than a century.1 Over the past decade, interest in this area has burgeoned because of recognition of higher-than-chance comorbidity rates of schizophrenia and obsessive-compulsive disorder (OCD), and observations of appearance or exacerbation of OCS during treatment of schizophrenia with atypical antipsychotics.2-6 Emerging neurobiological and genetic evidence suggests that persons with comorbid OCD and schizophrenia may represent a special category of the schizophrenic population.
The evidence for a putative schizo-obsessive disorder is examined and practical treatment suggestions for this subgroup of patients are outlined in this article.7-9
Comorbidity between OCD and schizophrenia
The lifetime prevalence for schizophrenia is 1% and for OCD it is 2% to 3%.10 Comorbidity rates for OCD in the schizophrenia population are substantially higher than what would be expected to occur randomly. In the schizophrenic population, the reported prevalence of clinically significant OCS and of OCD ranges from 10% to 52% and from 7.8% to 26%, respectively.11-23
The higher-than-expected comorbidity rate for OCD and schizophrenia suggests a nonrandom association and possibly an integral relation between these 2 conditions.9 The question is whether this comorbid group with schizo-obsessive disorder represents a more severely ill group with greater brain dysfunction that could, in part, be caused by common neurodevelopmental predisposing factors, or whether the 2 conditions are part of a more complex syndrome that represents a distinct diagnostic entity. The answer could be clarified in part if neurobiological studies were to demonstrate a distinct neuroanatomical substrate in this comorbid group rather than the summation or superimposition of neurobiological lesions observed in the separate disorders.9
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