Comparative neuropsychological function in obsessive-compulsive disorder and schizophrenia with and without obsessive-compulsive symptoms

Abstract

Executive function deficits are seen in both schizophrenia and obsessive-compulsive disorder (OCD), but research suggests that dorsolateral prefrontal (DLPF) dysfunction is associated with schizophrenia and orbitofrontal (OBF) dysfunction is associated with OCD. As part of a comprehensive europsychological assessment, the Bechara Gambling Task (BGT) was used to assess OBF function and the Wisconsin Card Sorting Test (WCST) was used to assess DLPF function among three groups: 26 individuals with schizophrenia/schizoaffective disorder with obsessive-compulsive symptoms (SCZ+), 28 individuals with schizophrenia/schizoaffective disorder without obsessive-compulsive symptoms (SCZ−), and, 11 individuals with OCD. It was predicted that the SCZ+ group and the OCD group would show impairments in OBF function, as compared to the SCZ− group, and that the SCZ+ and SCZ− groups would show impairments in DLPF function, as compared to the OCD group. It was also predicted that the SCZ+ group would perform more poorly than the SCZ− and OCD groups in a number of other cognitive domains. Contrary to expectation, no divergence between groups was seen on tests of executive function. Instead, there was a statistical trend for the SCZ+ and SCZ− groups, when combined, to perform worse than individuals with OCD on the measure of OBF. Although not significant at the designated alpha level, the profile results showed that the SCZ+ group performed slightly below the OCD and SCZ− groups across nearly all neuropsychological domains.

Introduction

There appears to be a higher than expected prevalence of obsessive-compulsive symptoms (OCS) in schizophrenia (25%–45%) than in the general population (3%), suggesting that the association between OCS and schizophrenia might be more than just comorbidity Berman et al., 1995, Berman et al., 1998, Myers et al., 1984. It is possible that when OCS are experienced in schizophrenia, the cognitive impairments associated with obsessive-compulsive disorder (OCD) add to or exacerbate existing cognitive impairments in schizophrenia. Exploratory studies have shown that people with schizophrenia with OCS (SCZ+) perform worse than people with schizophrenia without OCS (SCZ−) on certain neuropsychological tests, including measures of visuospatial skill, delayed non-verbal memory, vigilance, and executive functioning Berman et al., 1998, Hwang et al., 2000, Lysaker et al., 2002, Lysaker et al., 2000. The consequences of these increased cognitive impairments may be decreased social, community, and vocational functioning (Green, 1996). In fact, it been has shown that SCZ+ individuals spend more time in the hospital, need more support, are less likely to be married, and are less likely to be employed than SCZ− individuals (Berman et al., 1995).

Although observations of OCS in schizophrenia can be found among the earliest descriptions of the illness Bleuler, 1956, Kraepelin, 1919, Stengel, 1945, the issue has received little systematic study. A current theory holds that the basis for the overlap in symptom expression between the two disorders may lie in the overlap in proposed functional neuroanatomical circuits of obsessive-compulsive disorder (OCD) and schizophrenia (Tibbo and Warneke, 1999). While research suggests that there is a specific role of the dorsolateral prefrontal cortical (DLPF) circuit in schizophrenia and a specific role of the orbitofrontal (OBF) cortical circuit in OCD, it is known that these circuits share anatomic substrates, including the frontal lobe, striatum, globus pallidus, and thalamus. It is argued that that these circuits are generally segregated, but that there are projections to and from anatomic structures outside the defined circuit that may account for symptom comorbidity between the two disorders Cummings, 1993, Groenewegen et al., 1990, Parent, 1990. If this hypothesis is correct, then SCZ− individuals may show neuropsychological deficits reflecting DLPF dysfunction; OCD individuals may show OBF deficits on neuropsychological testing; and, SCZ+ individuals may show both sets of neuropsychological deficits.

Only two published studies, conducted by a single group of investigators, have compared the performance of individuals diagnosed with OCD to the performance of individuals diagnosed with schizophrenia on tests of executive function. Abbruzzese et al. (1995) compared executive functioning in inpatients with schizophrenia, OCD patients, and normal controls (25 per group). It was hypothesized that neuropsychological abnormalities seen in schizophrenia result from malfunctioning in the neurological circuits connecting the DLPF with basal ganglia, whereas thinking and motor abnormalities in OCD result from dysfunction in the circuits connecting the basal ganglia with the OBF cortex. In order to examine this hypothesis, the Wisconsin Card Sorting Test (WCST) was administered to assess DLPF functioning and the Object Alternation Test (OAT; Freedman and Oscar-Berman, 1986a, Freedman and Oscar-Berman, 1986b, Freedman, 1990) was administered to assess OBF functioning. As hypothesized, people with schizophrenia made more perseverative errors and more total errors on the WCST compared to people with OCD and normal controls; people with OCD made significantly more perseverative errors on the OAT compared to people with schizophrenia and normal controls. Members of the same research group have conducted two replications studies, which have demonstrated comparable results Abbruzzese et al., 1997, Cavallaro et al., in press.

In addition to the aforementioned studies, a single published study has examined executive functioning among individuals with schizophrenia spectrum symptoms and OCD symptoms (Spitznagel and Suhr, 2002). This study included four non-clinical groups: 18 participants with symptoms of schizotypal personality disorder, 14 participants with symptoms of OCD, 13 participants with symptoms of both schizotypal personality disorder and OCD, and 25 normal controls. Though the first three groups showed some clinical symptoms, they did not meet criteria for the psychiatric disorder. It was hypothesized that the OCD symptom group would demonstrate poor performance on tests of OBF function, the schizotypal group would demonstrate poor performance on tests of DLPF function, and the comorbid group would demonstrate poor performance on both tests of OBF and DLPF function. Participants were administered the WCST and the Delayed Response Test, which is a modified version of the OAT, to assess DLPF function. The OAT and the Delayed Alternation Test (DAT), another modified version of the OAT, were administered to assess OBF function. With regard to OBF function, results of the study were mixed. On the OAT, both the schizotypal and the OCD symptom group, but not the comorbid group, performed worse than controls. However, the OCD symptom group scored lower than the schizotypal group on the DAT, but not on the OAT. The latter finding led investigators to speculate that the OAT may be sensitive to, but not specific for, OBF impairment. With regard to DLPF function, contrary to expectation, neither the schizotypal group nor the comorbid group demonstrated impairments on neuropsychological tests thought to reflect DLPF function, as compared to controls or as compared to the OCD group.

The current study attempts to extend the findings of Abbruzzese et al., 1995, Abbruzzese et al., 1997 and Spitznagel and Suhr (2002) by concurrently examining executive function among individuals diagnosed with schizophrenia/schizoaffective disorder, individuals diagnosed with OCD, and comorbid individuals diagnosed with schizophrenia/schizoaffective disorder and also rated as having considerable OCD symptomatology. In the present study, it was hypothesized that the three groups (SCZ−, SCZ+, and OCD) would differ on neuropsychological tests associated with DLPF circuit and OBF circuit. Specifically, it was predicted that (1) neuropsychological dysfunction associated with the DLPF cortical circuit would be observed in the SCZ− and SCZ+ groups, but not in the OCD group, and (2) neuropsychological dysfunction associated with the OBF cortical circuit would be observed in the OCD and SCZ+ groups, but not in the SCZ− group. In addition, clinical neuropsychological literature has shown some evidence of impairments in visual spatial skills, visual memory, and attention in both OCD and in schizophrenia. This led to the ancillary hypothesis that (3) people with clinical symptoms of both disorders are expressing a pathophysiological double jeopardy; if so, the comorbid individuals could be expected to demonstrate greater levels of neuropsychological deficits in these shared areas of impairment. Therefore, it was hypothesized that the SCZ+ group would demonstrate greater levels of impairment in visual spatial skills, attention, visual memory, and, possibly, verbal memory than the OCD and SCZ− groups.