Cognitive Impairment in the Euthymic Phase of Chronic Unipolar Depression

Abstract

Cognitive functioning in the nonsymptomatic phase and the long-term cognitive outcome of patients with mood disorders are both heuristic and important clinical issues in the study of mood disorders. Literature findings are inconsistent because of design confounds. We tried to address these issues while controlling for several confounds including age, education, gender differences in neurobehavioral functioning, and diagnosis. Nonsymptomatic patients with a history of chronic unipolar depression and bipolar affective disorder and healthy male individuals were administered neuropsychological tests to assess attention, visual-motor tracking, executive abilities, and immediate verbal memory. Subjects had comparable depression scores at the time of testing. Disease duration was 7.5 years (SD 5.1) for unipolar and 11 years (SD 7.3) for bipolar patients. Unipolar patients were more impaired than healthy normal comparison subjects on measures of visual-motor sequencing (Trail Making Test A, p < .05), executive function (Trail Making Test B, Stroop Test Color/Word Trial, p < .05), and immediate memory and attention (CERAD 1st trial, WAIS Digit Symbol subtest, p < .05). Differences between bipolar patients and normal comparison subjects did not reach significance in any of the selected measures. Male patients with a history of chronic unipolar disorder are at risk for cognitive impairment in the nonsymptomatic phase of their disease. Cognitive disturbance is the type seen with prefrontal dysfunction and may be assessed with standard neuropsychological assessments.

Cognitive and neurological impairment in mood disorders

“…Still, a separate study showed that patients with a history of bipolar disorder who were euthymic when tested on the WCST committed more errors than did healthy controls [6]. Similarly, patients in either acute manic or euthymic mood states have demonstrated significant impairments on the Stroop Test [6,12,14]. Austin et al [13] showed that performance on the TMT-B was impaired for depressed patients and worsened with a patient's level of depression.…”

“…The Trail Making Test, Part A (TMT-A) [9] and the Digit Symbol Substitution Test (DSST) [10] involve attentional and working memory components. Unipolar depressed patients when acutely ill or when euthymic show deficits in both of these tasks [11][12][13]. In contrast, bipolar patients are unimpaired on the TMT-A [14][15].…”

“…Impairments have been reported during the depressed, manic, and euthymic phases of illness in tests of verbal memory, such as story recitation [6] and word list recall [12][13]15,18]. One study comparing depressed and euthymic patients versus healthy controls found an additional impairment for nonverbal memory, but only in acutely depressed patients, whereas the nonverbal memory performance for euthymic patients was comparable to that of controls [19].…”

“…As shown in the tables, one brain area named across cognitive domains is the DLPFC, and it appears to play a role in unipolar depression and bipolar disorder [47]. The pattern of cognitive impairment in these two disorders is similar, perhaps differing only in severity [12,48]. Therefore, it makes sense that these two disorders might share a common substrate in neurocognition, even though the two populations otherwise present very different clinical profiles.…”

Consensus paper of the WFSBP Task Force on Biological Markers: Biological Markers in Depression

“…Indeed, some studies have failed to demonstrate any residual memory impairment after clinical recovery, whereas others show persistent impairment, particularly in aspects of executive functioning (Beats et al 1996;Paradiso et al 1997). Thus, executive deficits could represent a relatively stable trait marker, whereas mnemonic impairment seems to be related to clinical state.…”