Cognitive impairment in early and late bipolar disorder.

BACKGROUND Late onset disorders are often associated with cerebral disfunctioning and cognitive impairment in elderly patients. It is unknown whether the age of onset affects cognition in patients with bipolar disorder. The authors compare cognition and clinical characteristics of early- and late-onset bipolar patients in a stable and euthymic condition. METHOD One hundred and nineteen older patients (age >60) with an early- (<40 years) or late-onset bipolar disorder and a group of 78 comparison subjects were extensively tested for cognitive functioning. RESULTS Bipolar subjects scored lower on most cognitive measures. The late-onset patients were more impaired in psychomotor performance and mental flexibility than the early-onset patients. These differences could not be explained by differences in exposure to cerebrovascular risk factors. CONCLUSIONS Older patients with bipolar disorder have substantial cognitive impairments. Late onset bipolar disorder is associated with more severe cognitive impairment than early-onset bipolar disorder. For clinical practice, it is important to develop treatment strategies which take this into account.