Cognitive impairment and dementia in bipolar disorder

In bipolar disorder (BD), impaired cognition has long been described as a psychopathological feature of abnormal mood states, or accepted as treatment related side-effects. More recently, neuropsychological studies conducted in older adults have led to the recognition that enduring, irreversible cognitive changes do occur in substantial proportion of euthymic patients with life-long BD, relevant enough to warrant the diagnosis of dementia. The increased risk for dementia in BD has been associated with older age and also with factors related to the clinical course of the disease. However, it is yet to be determined whether cognitive impairment and dementia represent a complication of the most severe cases, exacerbated by biological treatments and deprivations accumulated over years, or if should be viewed as part of the natural history of BD. In the present review, we revisit the epidemiological evidence of the association between BD and dementia, and discuss the putative mechanisms supporting this association. We hypothesize that dementia may be considered as a long-term feature of BD, which is exacerbated in the presence of other risk factors.