The impact of mood episodes and duration of illness on cognition in bipolar disorder

Objective: A number of studies showed cognitive impairment in bipolar patients but few researches have studied the impact of mood episodes or duration of illness on neuropsychological functioning. Methods: Cognitive functioning was examined in 110 bipolar 1 outpatients with different mood state (mania, major depression, mixed episode and euthymia). The neuropsychological battery included The Visual Search Test, Trail Making Test, Corsi Test, Frontal Assessment Battery (FAB), Cognitive Estimation Task (CET) and Tower of London and it assessed attention, memory and executive/planning functions. Failures in the different cognitive tests were compared between groups using chi(2) tests with Bonferroni's corrections. Finally a binary logistic regression was performed in order to find an eventual association between age and duration of illness and CET bizarreness. Results: All the symptomatic patients (manic, depressed, mixed) failed more frequently The Visual Search Test in comparison with euthymics (chi(2) = 9.882, df = 3, p = 0.017, phi = 0.30; rate of failures: manic patients 32.2%, depressed patients 30.6%, euthymics 0%, mixed patients 18.2%). CET was performed worse by manic and euthymic patients (chi(2) = 10.086, df = 3, p 0.015, phi = 0.31; rate of failures: manic patients 46.4%, depressed patients 22.9%, euthymics 52.1%, mixed patients 18.2%). Finally, a longer duration of illness was found to be predictive of more bizarreness at CET (OR = 1.06, p = 0.01). Conclusions: Bipolar patients present impairment in different cognitive domains even in euthymic phases. Frontal dysfunction might be associated with a long duration of illness as shown by number of bizarreness at CET in chronic bipolar patients.