Chapter 8
Schizophrenia and obsessive compulsive disorder
KEY POINTS
• Schizophrenia and OCD occur together much more commonly than would be expected by chance.
The association between schizophrenia and OCD is particularly fascinating in that there are both phenomenological and aetiopathogenic aspects. Some phenomena manifested as part of OCD can be quite bizarre and could be confused with psychotic symptoms. There is also evidence that some people with OCD go on to develop schizophrenia, whilst others manifest a disorder in which both OCD and schizophrenia symptoms are present: this is sometimes referred to as ‘schizo-obsessive’ disorder. Finally, a number of antipsychotic medications—notably clozapine—can exacerbate or even induce OCD symptoms in people with schizophrenia. Cheng et al. (2019) suggest five possible sequences for the association between schizophrenia and OCD, summarized in Box 8.1.
Box 8.1 Sequences of association of OCD and schizophrenia
• OCD occurring prior to schizophrenia
• OCD as part of a schizophrenia ‘at risk’ mental state
• OCD and schizophrenia onset at the same time
• OCD manifesting after the schizophrenia diagnosis
Adapted with permission from Cheng, Y. F., Chen, V. C. H., Yang, Y. H., et al. Risk of schizophrenia among people with obsessive-compulsive disorder: a nationwide population-based cohort study. Schizophrenia Research. Copyright © 2019 Elsevier B.V. All rights reserved.
How common is OCD in people with schizophrenia?
In the 1950s, Stengel recognized that people with schizophrenia are at increased risk of comorbid OCD, and his student Rosen (1957) duly reported a rate of OCD of 3.5% in a group of 848 people with schizophrenia. Those were the days when OCD was diagnosed very conservatively, and thus the reported rate was much higher than the general population rate. Subsequent studies have adopted more stringent methodology and larger samples, including non-clinical sampling frames. For example, using data from the US Epidemiological Catchment Area (ECA) study, Boyd and colleagues (1984) reported an Odds Ratio (OR) of 12.5 for OCD risk amongst people with schizophrenia, compared to the general population. Buckley et al. (2009) found 36 studies from a range of different settings (inpatient, day programme, community) and encompassing early episode and chronic schizophrenia samples: all bar one reported rates of OCD higher than those expected in the general population (range 0–32%). Higher rates tended to reflect the application of less stringent criteria for OCD in more recent editions of the DSM. Some studies avoided the diagnostic problem by simply reporting rates of OCS: here rates ranged from 10% to 60%.
Swets and colleagues (2014) performed a meta-analysis and meta-regression of 43 studies encompassing 3,978 individuals with schizophrenia and estimated a mean prevalence of OCD of 12.3%; for OCS the mean rate was 30.7%.
In terms of illness stage, features of OCD have been reported both in early and later stage schizophrenia. It is tempting to suggest that OCD is more common in people later on in the course of schizophrenia, but any such findings are highly inconsistent and in any event would be confounded by use of clozapine, which is mostly reserved for treatment-resistant schizophrenia and which has a strong signal for the induction of OCS. An excess of OCD has been shown in people at putative high risk for schizophrenia (DeVylder et al. 2012) as well as in the schizophrenia prodrome. Associations with comorbid OCD in schizophrenia are shown in Box 8.2.
Box 8.2 Features associated with schizophrenia in which OCD is comorbid
• Early onset of psychotic illness
• Cognitive dysfunction (notably executive function)
• Exposure to atypical antipsychotics, notably clozapine
Source: Data from Buckley, P., Miller, B.J., Lehrer, D.S., Castle, D.J. (2009) Psychiatric comorbidities and schizophrenia. Schizophrenia Bulletin, 35: 383–402; Poyurovsky, M., Kriss, V., Weisman, G., et al. (2005) Familial aggregation of schizophrenia-spectrum disorders and obsessive-compulsive associated disorders in schizophrenia probands with and without schizophrenia. American Journal of Medical Genetics B Neuropsychiatric Genetics, 133: 31–36; Hadi, E., Greenberg, Y., Sirota, P. (2012) Obsessive-compulsive symptoms in schizophrenia: prevalence, clinical features and treatment: a literature review. The World Journal of Biological Psychiatry, 13: 2–13.
How common is schizophrenia in people with OCD?
Whilst an excess of OCD in people with established schizophrenia has been widely reported, the issue of people who are initially diagnosed with OCD later manifesting schizophrenia has been less studied. The tracking of this sequence has important implications for our understanding of the pathophysiological underpinnings of the association between the two disorders. Longitudinal studies from Sweden (Cederlöf et al. 2015) and Denmark (Meier et al. 2014) have reported increased rates of schizophrenia in people diagnosed with OCD: 2.7-fold in the former and 6.9 (incidence ratio) in the latter study. Most recently, in a population cohort study from Taiwan, Cheng et al. (2019) found that the risk of later schizophrenia in people initially diagnosed with OCD (n=2,009) was 876.2 per 100,000 person years, whilst the risk in a non-OCD control sample (n=8,036: matched for age, sex, level of urbanization and income) was 28.7 per 100,000 person years. This represents an increased hazard in the OCD group of 30.2 (95% CI 17.9–51.2). Being male, having an OCD onset before age 20, comorbid autism spectrum disorder, and the prescription of antipsychotic medication were associated with a schizophrenia diagnosis. These associations suggest a profile of early onset, male preponderant neurodevelopmental deviance which increases risk for both schizophrenia and OCD and encompasses autism risk: this theory is expostulated in more detail below.
Why do schizophrenia and OCD occur together more often than by chance?
There are a number of theories as to why schizophrenia and OCD show such strong co-aggregation. Studies seeking a genetic explanation include that of Poyurovsky et al. (2005), which found an excess of both schizophrenia and OCD in the family members (n = 182) of probands with schizophrenia and OCD (n = 57) compared to those with schizophrenia alone (n = 60). These findings suggest some shared genetic predisposition to schizophrenia and OCD. Some commentators propose that there is a relatively discrete ‘schizo-obsessive’ subtype of schizophrenia, but one could equally argue for it being a subtype of OCD. Indeed, a neurodevelopmental subtype of OCD has long been hypothesized (e.g. Blanes and McGuire 1997): many features are shared with the putative neurodevelopmental subtype of schizophrenia (Murray et al. 1992): see Box 8.3.
Box 8.3 Shared features of putative neurodevelopmental subtypes of OCD and schizophrenia
• Poor premorbid social adjustment
• Poor premorbid academic achievement
Source: Data from Blanes, T., McGuire, P. (1997) Heterogeneity within obsessive-compulsive disorder: evidence for primary and neurodevelopmental subtypes. In: Keshavan MS, Murray RM (eds) Neurodevelopment and Adult Psychopathology. Cambridge: Cambridge University Press, pp. 206–212; Murray, R.M., O’Callaghan, E., Castle, D.J., Lewis, S.W. (1992) A neurodevelopmental approach to the classification of schizophrenia. Schizophrenia Bulletin, 18: 319–332.
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