Cognitive impairment in the remitted state of unipolar depressive disorder: A systematic review

Background: It is unclear whether cognitive impairment is prevalent in the remitted state of unipolar disorder. Aim: To evaluate whether cognitive function is impaired in the remitted state in patients with unipolar depression compared with healthy control individuals, and to investigate the association to prior course of illness, i.e. the number, duration and severity of prior depressive episodes. Method: Systematic search on existing on-line databases and hand-search of original published papers. Results: A total of 11 studies fulfilled the selection criteria and were included in the review, including a total of 500 patients remitted from unipolar depression and 471 healthy control individuals. In nine of the eleven studies performance on neuropsychological tests was found to be decreased in patients compared to healthy control individuals in at least one of the tests. Methodological drawbacks were prevalent including non-stringent definition of remission and non-correction for multiple testing. Only few studies investigated the association between cognition and prior course of illness and the results were divergent. Limitations: Stringent criteria were used in the assessment of eligibility of studies. The studies were first and foremost selected according to the criteria for remission used. Conclusion: Cognitive dysfunction seems to be present in individuals suffering from unipolar disorder in the remitted state. We recommend that future studies should focus on disentangling the state and trait characteristics of cognitive dysfunction in unipolar disorder and further clarify the associations with clinical phenotype, course of illness and subsyndromal psychopathology. Furthermore, there is a need to identify the cognitive difficulties in individuals suffering from unipolar disorder in relation to psychosocial function, quality of life and risk of recurrence and to assess the effect of treatment intervention on cognitive function. (C) 2010 Elsevier B.V. All rights reserved.