Long-term stability of cognitive impairment in bipolar disorder: a 2-year follow-up study of lithium-treated euthymic bipolar patients.

OBJECTIVE: To determine the course of cognitive impairment of bipolar disorder with a 2-year longitudinal study and to investigate whether the neuropsychological profile is related to clinical and psychosocial variables in a sample of lithium-treated euthymic bipolar outpatients.

METHOD: Thirty-three bipolar disorder patients (all of whom were diagnosed according to DSM-IV-TR criteria and were treated during 2003 at the Lithium Clinic Program at Santa Maria Hospital, Lleida, Spain) and 33 healthy, matched controls were cognitively assessed twice over a 2-year follow-up period. All patients were receiving the same mood-stabilizer pharmacotherapy (lithium) at the first evaluation, and they were euthymic (Hamilton Rating Scale for Depression score lower than 8 and Young Mania Rating Scale score lower than 6) for at least 3 months before both evaluations. Cognitive assessment was performed by means of a neuropsychological test battery tapping into the main cognitive domains (executive function, attention, processing speed, verbal memory, and visual memory).

RESULTS: Repeated-measures multivariate analysis of covariance showed that there were main effects of group in the executive domain (p < .04) and in processing speed (p < .04). Multiple linear regression analysis showed that none of the variables predicted psychosocial functioning (as measured with the Global Assessment of Functioning scale) (R(2) = 0.12, F = 2.08, p = .1). Multilevel logistic regression analysis showed that processing speed appeared to be significant as an indicator of low work activity (Exp[B] = 1.25, 95% CI = 1.005 to 1.547, p = .04).

CONCLUSIONS: Executive function and processing speed are the cognitive domains affected in euthymic bipolar outpatients, and such deficits are maintained over time. Our results show that executive dysfunction is the main long-term neuropsychological deficit of bipolar disorder. Slower processing seems to be related to worse work adaptation.