Schizophrenia is a leading cause of disability and one of the most devastating mental disorders. It is also relatively common, with a lifetime prevalence rate of about 0.4%.1 Symptomatic manifestations include distortions of reality such as delusions and hallucinations, disorganization of thought and behavior, negative symptoms, and cognitive impairment. Obsessive-compulsive disorder (OCD) is a mental illness with a lifetime prevalence rate of about 2.3%, and it has a distinct pathophysiology, clinical presentation, and treatment from schizophrenia.2 It is characterized by repetitive intrusive thoughts and compulsive behaviors associated with significant levels of subjective distress and interference with daily life.3
Shared Features of Schizophrenia and OCD
Neuroimaging studies have led to findings that several brain structures, including the cingulate cortex, prefrontal cortex, basal ganglia, and thalamus, are involved in the brain pathology of both disorders.4,5 Such findings suggest that schizophrenia and OCD may have neural underpinnings in common. Additionally, schizophrenia and OCD are known to share some key clinical and demographic features, meaning that some symptoms of one disorder are analogous to those of the other. For example, bizarre intrusive and persistent thoughts that occur in obsessions may be hard to distinguish from delusions, and the stereotypic behaviors and mannerisms of schizophrenia share similarities with the repetitive compulsive behaviors of OCD. Both disorders have chronic illness trajectory with periods of exacerbations and remissions, and they are both treated with psychotropic medications that act on serotonergic and dopaminergic systems. Age of onset is also comparable in both disorders. Furthermore, the prevalence rate of comorbid OCD or obsessive-compulsive symptoms (OCS; defined as existence of obsessions or compulsions below the threshold of OCD) in schizophrenia has been reported to be as high as 64%, which is much higher than the co-occurrence expected by chance, although there is much variation in this rate between studies.6,7 This discrepancy might be due to differences in definitions of OCS and OCD, and also due to the characteristics (eg, age, chronicity, treatment settings, and instruments used to measure symptom severity) of a sample population. Although the cause of this high comorbidity rate is not fully understood, it brought attention to the characteristics and clinical implications of this comorbidity. A meta-analysis8 examining the temporal relationship between onset of OCS and psychotic symptoms in patients with comorbid OCS and schizophrenia showed that onset of OCS precedes onset of psychotic symptoms in about one-half of patients (48%), a diagnosis of schizophrenia precedes onset of OCS in just less than one-third of patients (30%), and diagnoses of both disorders took place simultaneously in the remaining almost one-quarter (22%) of the patients. This evidence showing that development of OCS generally predates the onset of schizophrenia is consistent with epidemiologic data, given the slightly older age of onset in schizophrenia.8
Clinical Implications of OCS or OCD in Schizophrenia
Previous studies have examined several clinical implications of comorbid OCS or OCD in schizophrenia. Whereas some studies show mixed effects of comorbid OCS or OCD on positive symptom severity in schizophrenia,9–12 others indicate that patients with comorbid OCS/OCD and schizophrenia tend to have more severe negative symptoms.10,13 As negative symptoms in schizophrenia are more closely associated with functional outcome and prognosis, it follows that patients with schizophrenia with comorbid OCS/OCD, and therefore more severe negative symptomatology, are more likely to have greater functional impairment, worse quality of life, and higher frequency of suicide attempts.14 A meta-analysis regarding the impact of OCS and OCD on the severity of psychotic symptoms in schizophrenia was conducted to further elucidate this effect.15 The meta-analysis indicated that the comorbidity of OCS in patients with schizophrenia was associated with greater severity of global, positive, and negative psychotic symptoms. However, this effect was not observed when the categorical definition of OCD was used, with comorbid OCD in schizophrenia showing no difference in the severity of global, positive, and negative psychotic symptoms when compared with a control group of patients with schizophrenia without comorbid OCD.
The Association between OCS or OCD and Cognitive Function in Schizophrenia
Cognitive dysfunction is considered a core feature of schizophrenia. Cognitive impairment in schizophrenia is known to range from moderate to severe across most cognitive domains, including working memory, verbal learning and memory, attention/vigilance, processing speed, and executive functions.16,17 Patients with OCD also have cognitive deficits compared to healthy controls, especially in visuospatial memory and executive functioning, although their cognitive impairment is generally not very substantial.18 High comorbidity rates of OCS or OCD in schizophrenia have led to the suggestion that patients with schizophrenia with comorbid OCS or OCD would show worse performance in those same cognitive domains in which patient with OCD display deficits, namely visuospatial memory, processing speed, and executive functioning.19
Based on this hypothesis, a number of studies have evaluated the relationship between comorbid OCS or OCD and cognitive impairment in patients with schizophrenia, but the results have been inconsistent. Some studies found that comorbid OCS or OCD was associated with worse performance in cognitive domains such as executive functioning,10,20–21 whereas other studies found no evidence of differences in cognitive functioning between patients with schizophrenia with or without comorbid OCS or OCD.23,24 A few studies even reported that patients with schizophrenia with comorbid OCS had improved performance in certain cognitive tasks.25,26 Furthermore, people at high risk for psychosis with OCS performed better on some cognitive tests than did those without OCS.27
The inconsistency in these findings may be explained by varying study populations, diversity of OCS in schizophrenic illness, small sample size, use of healthy control groups, differences in cognitive tasks used, or types of antipsychotics used by the participants.28,29 In addition, other factors that are known to influence cognitive functioning, such as age, age of onset of illness, and severity of psychotic symptoms, could also contribute to the mixed findings.28 Indeed, Michalopoulou et al.28 controlled for these factors (ie, age, years of education, and severity of psychotic symptoms) and examined whether the presence of comorbid OCS was linked to worse performance in cognitive domains such as processing speed and executive functions. They found decreased performance in processing speed in patients with schizophrenia with comorbid OCS as compared to patients with schizophrenia without OCS, and this effect was independent of the severity of OCS. To control for the confounding effects of antipsychotic medications, another recent study only included patients with schizophrenia who received risperidone monotherapy.29 The authors found more severe psychotic and depressive symptoms in patients with schizophrenia with comorbid OCS; however, these patients did not show significant deficits in cognitive functioning compared to those without comorbid OCS. Overall, the impact of comorbid OCS or OCD on cognitive functioning in schizophrenia remains unclear.
Most studies examining the relationship between cognitive impairment and comorbid OCS or OCD in schizophrenia are designed as cross-sectional studies. The cross-sectional associations between cognitive impairment and OCS make it difficult to ascertain whether cognitive deficits function as risk factors for development of comorbid OCS or follow as a consequence of comorbid OCS.30 Longitudinal studies could produce findings that form building blocks for a better understanding of the causality relationship. A few studies have prospectively evaluated cognitive functioning in patients with schizophrenia with comorbid OCS. In a study by Lysaker et al.,31 patients with schizophrenia completed executive function testing and clinical assessments at baseline and at 6-month follow-up. The authors found that worse performance in inhibition switching was associated with increased OCS burden at both assessments. Another study found that patients with schizophrenia with comorbid OCS exhibited cognitive deficits in tasks measuring visuospatial perception and memory, cognitive flexibility, and immediate verbal learning over a 12-month assessment period.22 Recently, a large longitudinal, multicenter study included unaffected first-degree relatives as well as patients with psychotic disorders to examine whether cognitive deficits precede the clinical onset of OCS.30 The authors did not find any evidence of cognitive risk preceding the development of OCS in patients with psychotic disorders or their first-degree relatives. Instead, they found that remission of comorbid OCS in patients and relatives had significant association with cognitive improvement in processing speed and immediate verbal recall, supporting the notion that cognitive deficits are the result of OCS. Overall, there is considerable heterogeneity in both cross-sectional and longitudinal associations of comorbid OCS or OCD with cognitive impairment in schizophrenia. Thus, the question of whether the cognitive deficits are underlying endophenotypes for the development of co-occurring OCS or the deficits result from OCS in schizophrenia remains unclear and requires further investigation.
Previous studies have found that schizophrenia and OCD share a number of features, including brain structural abnormality, phenomenology, clinical course, and demographic characteristics. The high prevalence of comorbid OCS or OCD in schizophrenia has received increased attention because of its association with more severe clinical symptoms, worse functional outcomes and prognosis, and cognitive impairment. Specifically, it has been suggested that patients with schizophrenia with comorbid OCS or OCD exhibit worse performance in specific cognitive domains, such as executive functioning, as patients with OCD often display deficits in these domains. However, the findings to date have been inconsistent due to several confounding variables and heterogeneity across populations. Therefore, it remains unclear as to whether cognitive deficits in schizophrenia are risk factors for development of comorbid OCS or OCD, or whether impaired cognitive functioning is a consequence of OCS or OCD comorbidity. Future prospective studies are necessary to clarify the associations of comorbid OCS or OCD with cognitive deficits in schizophrenia, which can be used to further understand the underlying pathogenesis and develop effective management strategies for this population.
- McGrath J, Saha S, Chant D, Welham J. Schizophrenia: a concise overview of incidence, prevalence, and mortality. Epidemiol Rev. 2008;30:67–76. doi:. doi:10.1093/epirev/mxn001 [CrossRef]
- Ruscio AM, Stein DJ, Chiu WT, Kessler RC. The epidemiology of obsessive-compulsive disorder in the National Comorbidity Survey Replication. Mol Psychiatry. 2010;15(1):53–63. doi:. doi:10.1038/mp.2008.94 [CrossRef]
- American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 5th ed. Arlington, VA: American Psychiatric Publishing; 2013.
- Abbruzzese M, Ferri S, Scarone S. The selective breakdown of frontal functions in patients with obsessive-compulsive disorder and in patients with schizophrenia: a double dissociation experimental finding. Neuropsychologia. 1997;35(6): 907–912. doi:10.1016/S0028-3932(96)00095-4 [CrossRef]
- Gross-Isseroff R, Hermesh H, Zohar J, Weizman A. Neuroimaging communality between schizophrenia and obsessive compulsive disorder: a putative basis for schizo-obsessive disorder?World J Biol Psychiatry. 2003;4(3):129–134. doi:. doi:10.1080/15622970310029907 [CrossRef]
- Fabisch K, Fabisch H, Langs G, Huber HP, Zapotoczky HG. Incidence of obsessive-compulsive phenomena in the course of acute schizophrenia and schizoaffective disorder. Eur Psychiatry. 2001;16(6):336–341. doi:. doi:10.1016/S0924-9338(01)00588-0 [CrossRef]
- Kayahan B, Ozturk O, Veznedaroglu B, Eraslan D. Obsessive-compulsive symptoms in schizophrenia: prevalence and clinical correlates. Psychiatry Clin Neurosci. 2005;59(3):291–295. doi:. doi:10.1111/j.1440-1819.2005.01373.x [CrossRef]
- Devulapalli KK, Welge JA, Nasrallah HA. Temporal sequence of clinical manifestation in schizophrenia with co-morbid OCD: review and meta-analysis. Psychiatry Res. 2008;161(1):105–108. doi:. doi:10.1016/j.psychres.2008.01.013 [CrossRef]
- de Haan L, Hoogeboom B, Beuk N, Wouters L, Dingemans PM, Linszen DH. Reliability and validity of the Yale-Brown obsessive-compulsive scale in schizophrenia patients. Psychopharmacol Bull. 2006;39(1):25–30.
- Hwang MY, Morgan JE, Losonczy MF. Clinical and neuropsychological profiles of obsessive-compulsive schizophrenia: a pilot study. J Neuropsychiatry Clin Neurosci. 2000;12:91–94. doi:. doi:10.1176/jnp.12.1.91 [CrossRef]
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- Poyurovsky M, Hramenkov S, Isakov V, et al. Obsessive-compulsive disorder in hospitalized patients with chronic schizophrenia. Psychiatry Res. 2001;102(1):49–57. doi:10.1016/S0165-1781(01)00238-4 [CrossRef]
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