Comorbidity of mild cognitive disorder and depression--a neuropsychological analysis

Mild cognitive impairment is found in many cases of depression, and it is mostly assumed to improve during the time course of depression remission. Recent data question the reversibility of low cognitive test performance in depression. The aim of this study is to determine the degree of reversibility and the proportion of patients who will not demonstrate reversibility of cognitive dysfunction. Consecutive inpatients suffering from depression (N=102) were investigated and N=82 matched control subjects. N=57 of the patients were diagnosed as major depression according to DSM-IV. A total of N=67 could be retested after remission of depression (N=32 of the patients with major depression) and a matched control group (N=62). Neuropsychological tests were applied in a test session which avoids the effects of fatigue in the patients by the short duration of strenuous tests. For most neuropsychological tests an impaired performance in the depressed patients was found. About one third of the depression subjects performed at an impaired level in tests of averbal memory and verbal fluency (below 5th percentile). In the follow-up investigation, a slight improvement in performance could be assessed for both the depression and the control group, which was, however, attributed to a general test training effect. No normalization of cognitive test performance was found in spite of complete recovery of the affective symptoms. No correlation between the duration of the disease before the index episode or number of episodes and cognitive deficits could be found. The data of the neuropsychological deficits of depressed patients, which are stable in the time course of the affective disorder, may indicate that these patients may suffer from comorbidity of both depression and mild cognitive disorder. The findings are discussed as 1) indicating only a minor impact of the depressed mood on the cognitive performance and 2) they are consistent with a role of brain lesions which have been reported in several studies in a subgroup of depression.