Status of Type II vs. Type I Bipolar Disorder: Systematic Review with Meta-Analyses

• Analyze and compare the different bipolar disorder (BD) types.• Identify markers that distinguish BD types and explain how the DSM-IV defines the disorder.

Since the status of type II bipolar disorder (BD2) as a separate and distinct form of bipolar disorder (BD) remains controversial, we reviewed studies that directly compare BD2 to type I bipolar disorder (BD1). Systematic literature searching yielded 36 reports with head-to-head comparisons involving 52,631 BD1 and 37,363 BD2 patients (total N = 89,994) observed for 14.6 years, regarding 21 factors (with 12 reports/factor). BD2 subjects had significantly more additional psychiatric diagnoses, depressions/year, rapid cycling, family psychiatric history, female sex, and antidepressant treatment, but less treatment with lithium or antipsychotics, fewer hospitalizations or psychotic features, and lower unemployment rates than BD1 subjects. However, the diagnostic groups did not differ significantly in education, onset age, marital status, [hypo]manias/year, risk of suicide attempts, substance use disorders, medical comorbidities, or access to psychotherapy. Heterogeneity in reported comparisons of BD2 and BD1 limits the firmness of some observations, but study findings indicate that the BD types differ substantially by several descriptive and clinical measures and that BD2 remains diagnostically stable over many years. We conclude that BD2 requires better clinical recognition and significantly more research aimed at optimizing its treatment.