The association of duration and severity of disease with executive function: Differences between drug-naïve patients with bipolar and unipolar depression

Background: The aims of this study were to investigate the differences in executive function and the relationship with clinical factors between drug-naïve patients with bipolar depression (BDD) and unipolar depression (UPD).

Methods: Drug-naïve patients with BDD, UPD and healthy controls (HC) were recruited (30 cases in each group). All patients were assessed with Hamilton Rating Scale for Anxiety (HAM-A), Hamilton Rating Scale for Depression-17 (HAM-D), and Young Mania Rating Scale (YMRS). Executive function was evaluated by Stroop color-word test (CWT) and Wisconsin Card Sorting Test (WCST).

Results: In the BDD group, only the CWT number of missing was higher than HCs (P = 0.047). In the UDP group, CWT number of correct was lower, CWT number of missing was higher, and the WCST indices were worse than the HC group (P < 0.05). The WCST percentage of errors (PE) and percentage of conceptual level responses (PCLR) in the UPD group were worse than the BDD group (P < 0.05). In the BDD group, no correlations between CWT and WCST indices and clinical features were detected after correcting for multiple comparisons (P > 0.05). In the UDP group, the WCST PE, PCLR, number of categories completed (CC), and the percentage of perseverative responses (PPR) were correlated to the number of mood episodes (P < 0.01).

Limitation: This was a small-sample cross-sectional study. The possibility of UPD transforming to bipolar disorder (BD) in future could not be ruled out.

Conclusion: Our results suggested only small differences in executive function between drug-naïve patients with BDD and UPD, but in this sample only the UPD group showed differences with HCs. The executive function of drug-naïve BDD patients may be associated with duration of current depressive episode, while for UDP patients executive function indices were significantly correlated with number of mood episodes.