American tertiary clinic-referred bipolar II disorder compared to bipolar I disorder : more severe in multiple ways, but less severe in a few other ways

Background Prevalence and relative severity of bipolar II disorder (BDII) vs. bipolar I disorder (BDI) are controversial. Methods Prevalence, demographics, and illness characteristics were compared among 260 BDII and 243 BDI outpatients referred to the Stanford University BD Clinic and assessed with the Systematic Treatment Enhancement Program for Bipolar Disorder Affective Disorders Evaluation. Results BDII vs. BDI outpatients had statistically similar prevalence (51.7% vs. 48.3%), and in multiple ways had more severe illness, having significantly more often: lifetime comorbid anxiety (70.8% vs. 58.4%) and personality (15.4% vs. 7.4%) disorders, first-degree relative with mood disorder (62.3% vs. 52.3%), at least 10 prior mood episodes (80.0% vs. 50.9%), current syndromal/subsyndromal depression (52.3% vs. 38.4%), current antidepressant use (47.3% vs. 31.3%), prior year rapid cycling (33.6% vs. 13.4%), childhood onset (26.2% vs. 16.0%), as well as earlier onset age (17.0±8.6 vs. 18.9±8.1 years), longer illness duration (19.0±13.0 vs. 16.1±13.0), and higher current Clinical Global Impression for Bipolar Disorder-Overall Severity (4.1±1.4 vs. 3.7±1.5). However, BDII vs. BDI patients significantly less often had prior psychosis (14.2% vs. 64.2%), psychiatric hospitalization (10.0% vs. 67.9%), and current prescription psychotropic use, (81.5% vs. 93.0%), and had a statistically similar rate of prior suicide attempt (29.5% vs. 32.1%). Limitations American tertiary bipolar disorder clinic referral sample, cross-sectional design. Conclusions Further studies are warranted to determine the extent to which BDII, compared to BDI, can be more severe in multiple ways but less severe in a few other ways, and contributors to occurrence of more severe forms of BDII.