Schizophrenia is a heterogeneous disorder. Given the absence of biological markers, and accurate definition of a phenotype is required for improved understanding of its etiology, better treatment strategies and predicting outcome. According to Robins and Guze, clinical description, delimitation from other disorders, follow-up and family studies are especially important for establishing the diagnostic validity of psychiatric syndromes.
Kendler expanded these criteria to include antecedent validators (e.g. familial inheritance, premorbid personality), concurrent validators (e.g. psychological and biological tests) and predictive validators (e.g. diagnostic consistency, functioning over time, treatment response). Within this framework, there is considerable evidence suggesting that schizophrenia with OCS/OCD has unique clinical characteristics (a combination of schizophrenic and obsessive-compulsive symptoms), distinct treatment response (limited efficacy of typical antipsychotics and favorable response to adjunctive SSRIs) and relatively poor prognosis.
The next logical step to further discriminate between OCD and non-OCD schizophrenia subgroups is a family study evaluating the rate of occurrence of obsessive-compulsive phenomena (OCS, OCD) in first degree relatives of schizophrenia probands with and without OCD. It would also be interesting to determine if familiality extends beyond OCD. To do so, we would need to evaluate familial aggregation of the so-called OCD-spectrum disorders that appeared to co-occur with OCD in both patients with OCD and their first-degree relative
Indeed, earlier studies have reported higher rates of trichotillomania body dysmorphic disorder and chronic tic disorder in schizophrenia patients with OCD compared with their non-OCD counterparts, indicate a possible common pathophysiological. The mechanism underlying these disorders and OCD.
An integrative approach including phenotype determination, neurocognitive evaluation, brain imaging and genetic studies in schizophrenia patients with and without OCD could lead to better validation of the schizophrenia-OCD diagnostic entity and phenotype/genotype interaction.
Finally, the identification of subgroups of schizo-obsessive patients with either typical ego-dystonic OCD or more delusion-related OCS indicates a substantial heterogeneity of this patient population. It is possible that within the schizophrenia-OCD entity, ego-dystonic OCD may represent a distinct comorbid disorder and delusion-related OCD may represent a specific dimension of schizophrenia. Further characterization of these subgroups in terms of course of illness, prognosis, and response to pharmacological interventions may shed further light on the interrelationship between OCD and schizophrenia in this unique population.