Objectives: The aim of this study was to compare the neuropsychological performance of patients with bipolar or unipolar mood disorders during acute episodes of depression using intelligence and frontal lobe tests.
Methods: Fifteen patients with bipolar depression (BP) and 30 with unipolar depression (UP) were studied. For the neuropsychological assessment, the following tests: the Wechsler Adult Intelligence Scale-Revised (WAIS-R), the Trail Making Test (TMT), the Stroop test, the verbal fluency test and the Wisconsin Card Sorting Test (WCST) were used.
Results: The mean intensity of depression and mean duration of illness were similar in both groups. Patients in the BP group achieved significantly lower levels of performance in the non-verbal part of WAIS-R, in both parts of the Stroop test, in the verbal fluency test and also showed a tendency to achieve poorer results in TMT-B than those in the UP group. Bipolar depressed patients also produced significantly poorer results with the WCST as they made twice as many perseverative errors and only completed half of the correct categories compared with the UP patients. The results of the TMT-A tests, which measure psychomotor slowness, were similar in BP and UP patients. No differences between the results of male and female patients were noted in either group. Deterioration of the results associated with duration of the illness was only observed in the UP patients.
Conclusions: A higher degree of cognitive dysfunction connected with frontal lobe activity during an acute depressive episode was found in bipolar compared with unipolar depressed patients. These results may corroborate other findings pointing to pathogenic distinctions between bipolar and unipolar affective illness and to some similarities between bipolar illness and schizophrenia.