The Frontal Lobe Neuropsychological Tests in Patients With Schizophrenia and/or Obsessive-Compulsive Disorder

The study included 60 subjects divided into four groups (Table 1):

Fifteen schizophrenic patients without OC symptoms (S), 8 male, 7 female, age 33+10y;

Thirteen schizophrenic patients with OC symptoms (S-OC), 8 male, 5 female, age 26+6y);

Seventeen patients with OCD, 10 male, 7 female, age 29+9y; and

Fifteen healthy control subjects (C), 6 male, 9 female, age 30+9y

Informed consent was obtained from all subjects, following a complete description of the procedure. All patients were treated at the inpatient or outpatient unit in the, Department of Psychiatry, University School of Medicine in Bydgoszcz, Poland. None of the patients had a history of substance abuse, neurological illness, or serious somatic illness. The diagnoses were made by psychiatric staff, using ICD-10 and DSM-IV criteria. All patients from group 1 and group 2 met the criteria for schizophrenia, and patients from group 2 fulfilled the additional criteria for OCD. OCD was the primary diagnosis for patients in group 3, none of which had concomitant psychiatric comorbidity (“pure” OCD). Control subjects were recruited from clinical staff or medical students. They were somatically healthy, and neither they nor their first-degree relatives had psychiatric or neurological illnesses.

Psychometric assessment of the intensity of schizophrenic symptoms was done using the Positive and Negative Symptoms Scale (PANSS), while the assessment of OC symptoms was conducted using the Yale Brown Obssessive-Compulsive Scale (Y-BOCS). At the time of investigation, all patients showed a moderate exacerbation of symptoms.

The assessment of cognitive functions was performed using selected neuropsychological tests:

Table 1 shows clinical data, the intensity of psychopathological symptoms, and the results of neuropsychological tests in four groups of subjects studied.

Differences between groups regarding the duration of illness and level of education were not observed. Schizophrenic patients with or without OC symptoms had a similar intensity of symptoms, as measured by the PANSS scale (total and negative symptoms). Additionally, no difference in the intensity of OC symptoms measured by the Y-BOCS was found between patients with OCD and patients with schizophrenia accompanied by symptoms of OC.

On each test, the neuropsychological performance of all three patient groups was significantly poorer than that of control subjects. In TMT A tests and TMT B tests, a significantly improved performance was observed in OCD patients, as compared with both groups of schizophrenic patients (with or without OC symptoms). Among schizophrenic patients, however, those who had symptoms of OC performed better.

On the Stroop test, significant differences between OCD patients and healthy subjects were not found, and no significant differences were observed between schizophrenic patients with or without OC symptoms. However, schizophrenic patients had significantly worse results compared with OCD patients and control subjects, especially in Part B of the test.

All investigated patient groups demonstrated lower verbal fluency performance than healthy control subjects. Among schizophrenic patients, perseverations scores were worse in those without OC symptoms.

The performance of all three subject groups was significantly worse than that of healthy control subjects. These results are comparable with other neuropsychological studies that underscore frontal pathology in both schizophrenia and OCD.^6–8 However, on all assessments that were conducted, patients with OCD performed significantly better than patients with schizophrenia.

On tests measuring frontal lobe function, comparison of schizophrenic patients with or without OC symptoms revealed that OC schizophrenics scored either better than (TMT B, perseverations in VF) or similar (Stroop B) to schizophrenic patients without OC symptoms. Therefore, the main finding of our study reveals that, if groups of patients are matched for level of education and duration of illness, S-OC patients will show that they fall between “pure” schizophrenia and “pure” OCD, as identified on frontal lobe tests. This finding corroborates the results of studies that show some “protective” effect of OC symptoms on frontal impairment in schizophrenia.² In recent molecular genetic studies, common predisposing genes were postulated for both schizophrenia and OCD in S-OC patients; thus, a possibility for the comorbidity of these illnesses exists.^11,13

To reconcile our findings with those of Hwang et al.,³ we propose that the effect of OC symptoms (or OCD comorbidity) in schizophrenia may depend on the stage of the illness. In the early stage of schizophrenia, OC symptoms may have an alleviating effect. The Poyurovsky et al.² study included first-episode schizophrenic patients. The mean duration of illness in subjects used in our study was 7 years. The duration of illness in participants of the Hwang et al.³ study was not given but may have been much longer than 7 years because chronic schizophrenic patients were included. It is possible that during chronic course, the (untreated) OC symptoms may further add to the deterioration of the clinical picture of schizophrenia. We could also speculate that early treatment of OC symptoms in schizophrenia may have a beneficial effect on the longitudinal course of the illness.