Functional impairment in bipolar II disorder: is it as disabling as bipolar I?

It is well established that patients with bipolar disorder experience functional impairment even in remission. Nevertheless, bipolar II disorder remains understudied because most investigations to date include only bipolar I patients or just a small sample of bipolar II patients, without explicitly comparing both subtypes of disorder. The main objective of the current report is to evaluate overall and multiple domains of functioning, specifically in bipolar II disorder compared to patients with bipolar I disorder and healthy subjects.

233 subjects from 3 groups were compared: bipolar I patients (n=106), bipolar II patients (n=66) and healthy controls (n=61). Bipolar patients meeting criteria of remission were recruited at the Hospital Clinic of Barcelona and at different study sites in Argentina. All participants were assessed with 17-item Hamilton Depression Rating Scale (HAM-D), Young Mania Rating Scale (YMRS) and the Functioning Assessment Short Test (FAST). Clinical and sociodemographic data were also recorded.

Both subgroups of patients, bipolar I and bipolar II, showed lower overall functioning (p<0.001) and in each domain of the FAST scale (all, p<0.001) when compared to the healthy control group. Tukey post hoc test revealed that bipolar II patients scored worse in the cognitive domain compared to bipolar I patients. However, after controlling for potential confounding variables, this difference disappeared and only older age (p<0.005) and HAM-D scores (p<0.001) remained significant.

Our results suggest that bipolar II patients are as disabled as bipolar I patients. This may be explained, in part, because bipolar II patients experience greater lifetime residual depressive symptoms than the bipolar I subgroup, which may have particular impact on cognitive domains of functioning.