Similar profiles of cognitive domain deficits between medication-naïve patients with bipolar II depression and those with major depressive disorder.

BACKGROUND

Bipolar disorder (BD) II is more likely to be misdiagnosed as major depressive disorder (MDD) than other types of BD, leading to incorrect treatment and poor outcomes. Previous studies have shown inconsistent results regarding the differences in cognitive deficits between the two disorders. To eliminate the compounding effects of medication and aging, we sought to investigate changes in cognitive function in medication-naïve, non-late-life patients with BDII and MDD.

METHODS

Three subject groups were enrolled: 30 depressed BDII patients, 30 depressed MDD patients and 30 healthy controls. All subjects underwent a battery of cognitive tests to assess 8 cognitive domains. The cognitive domains were compared between the three subject groups. In BDII and MDD, the effect sizes were computed as evaluation parameters, weighing the degree of the cognitive deficits and the correlations between cognitive test deficits and clinical variables were also computed.

RESULTS

Compared with the controls, the BDII and MDD patients were characterized by similar deficits in psychomotor speed, working memory, visual memory, attention switching and verbal fluency. Moderate to severe deficits in the majority of cognitive tests were observed in the BDII and MDD patients. Furthermore, correlations between the modified Wisconsin Card Sorting Test total errors and age of onset in the BDII patients and between correct digit span responses (backward and total) and depressive severity were found in the MDD patients.

CONCLUSIONS

Our findings suggest that BDII and MDD patients may suffer from similar profiles of cognitive domain deficits that may not assist in distinguishing between the two disorders. In addition, cognitive deficits may be correlated with the age of onset and depressive severity in mood disorders.