A longitudinal study of cognition in asymptomatic and mildly symptomatic bipolar disorder patients

Bipolar disorder (BD) is characterized by cognitive deficits that impair patients' functioning and quality of life. Most of the earlier studies assessing changes in BD patients' cognitive functioning over time utilized a cross-sectional research design. The few longitudinal studies that were conducted tended to have methodological limitations such as very short follow-up periods, recruitment of acutely ill patients, and lack of assessment of practice effects. The current study aimed to assess changes over time in the cognitive functioning of typical BD outpatients. For this purpose, asymptomatic and mildly symptomatic BD outpatients were assessed at baseline and after two years (n=31). At baseline, the cognitive functioning of the BD patients was compared to that of gender- and age-matched healthy controls. Practice effects were estimated by re-assessing the controls one week after their first assessment. Compared to the controls, BD patients had deficits in psychomotor speed, sustained attention, and one domain of executive functioning (cognitive planning). No evidence was found of a decline in their cognitive functioning over the two year time interval. These findings support a developmental model of cognitive impairment in BD. Studies using longer follow-up periods and larger sample sizes, however, are needed before these conclusions can be stated confidently.