Subthreshold Hypomanic Symptoms in Progression From Unipolar Major Depression to Bipolar Disorder

OBJECTIVE: The authors assessed whether subthreshold hypomanic symptoms in patients with major depression predicted new-onset mania or hypomania. METHOD: The authors identified 550 individuals followed for at least 1 year in the National Institute of Mental Health Collaborative Depression Study with a diagnosis of major depression at intake. All participants were screened at baseline for five manic symptoms: elevated mood, decreased need for sleep, unusually high energy, increased goal-directed activity, and grandiosity. Participants were followed prospectively for a mean of 17.5 years and up to 31 years. The Longitudinal Interval Follow-up Examination was used to monitor course of illness and to identify any hypomania or mania. The association of subthreshold hypomanic symptoms at baseline with subsequent hypomania or mania was determined in survival analyses using Cox proportional hazards regression. RESULTS: With a cumulative probability of one in four on survival analysis, 19.6% (N=108) of the sample experienced hypomania or mania, resulting in revision of diagnoses for 12.2% to bipolar II disorder and 7.5% to bipolar I disorder. Number of subthreshold hypomanic symptoms, presence of psychosis, and age at illness onset predicted progression to bipolar disorder. Decreased need for sleep, unusually high energy, and increased goal-directed activity were specifically implicated. CONCLUSIONS: Symptoms of hypomania, even when of low intensity, were frequently associated with subsequent progression to bipolar disorder, although the majority of patients who converted did not have any symptoms of hypomania at baseline. These results suggest that continued monitoring for the possibility of progression to bipolar disorder is necessary over the long-term course of major depressive disorder.