Abstract
BackgroundCognitive dysfunction is clearly recognized in bipolar patients, but the degree of impairment varies due to methodological factors as well as heterogeneity in patient populations. The goal of this study was to evaluate cognitive functioning in bipolar patients and to assess its association with depressive symptoms. Post hoc the relationship with lifetime alcohol use disorder was explored.Methodology/Principal FindingsThe study included 110 bipolar patients and 75 healthy controls. Patients with severe depressive symptoms, (hypo)manic symptoms and current severe alcohol use disorder were excluded. Diagnoses were evaluated via the Mini-International Neuropsychiatric Interview. Cognitive functioning was measured in domains of psychomotor speed, speed of information processing, attentional switching, verbal memory, visual memory, executive functioning and an overall mean score. Severity of depression was assessed by the Inventory of Depressive Symptomatology-self rating. Patients were euthymic (n = 46) or with current mild (n = 38) or moderate (n = 26) depressive symptoms. Cognitive impairment was found in 26% (z-score 2 or more above reference control group for at least one domain) of patients, most prominent in executive functioning (effect size; ES 0.49) and speed of information processing (ES 0.47). Depressive symptoms were associated with dysfunction in psychomotor speed (adjusted beta 0.43; R2 7%), speed of information processing (adjusted beta 0.36; R2 20%), attentional switching (adjusted beta 0.24; R2 16%) and the mean score (adjusted beta 0.23; R2 24%), but not with verbal and visual memory and executive functioning. Depressive symptoms explained 24% of the variance in the mean z-score of all 6 cognitive domains. Comorbid lifetime alcohol use (n = 21) was not associated with cognitive dysfunction.Conclusions/SignificanceCognitive dysfunction in bipolar disorder is more severe in patients with depressive symptoms, especially regarding speed and attention. Therefore, interpretation of cognitive functioning in patients with depressive symptoms should be cautious. No association was found between cognitive functioning and lifetime comorbid alcohol use disorder.
Highlights
During mood episodes [1,2,3], as well in euthymic phases [4,5] bipolar patients show cognitive impairment in several neuropsychological domains
Sometimes clinicians may request for a neuropsychological assessment, since wellknown social and occupational problems in bipolar patients [12,13,14] partly seem to be due to cognitive impairment [15,16,17,18,19,20,21]
In a post hoc analysis we explored the association of cognitive functioning with lifetime alcohol use disorder
Summary
During mood episodes [1,2,3], as well in euthymic phases [4,5] bipolar patients show cognitive impairment in several neuropsychological domains. The degree of cognitive impairment varies extensively across studies due to methodological factors as well as the heterogeneity of illnesses and patient characteristics [3,4,6,7,8,9,10,11], as commonly seen in daily clinical practice. Research looking for putative cognitive endophenotypes [6,8,22] explicitly rules out patients characterized by commonly seen illness characteristics, and thereby limits the generalizability of these study results; after all bipolar patients are known to be euthymic for not more than 50% of time [23,24,25] and many suffer from comorbid substance use disorders, mostly alcohol misuse [26,27]. Post hoc the relationship with lifetime alcohol use disorder was explored
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