A comparison of the age of onset of bipolar I and bipolar II outpatients

Background: It is not clear if bipolar I and bipolar II disorders are variants of the same disorder or distinct disorders. Aim of the study was to compare age at onset and indicators of severity (recurrences, chronicity, psychosis) between bipolar I and bipolar ii disorders to clarify this point. Methods: Consecutive 45 bipolar I and 141 bipolar II outpatients were interviewed with the Structured Clinical Interview for DSM-IV. Age at onset distributions were compared with the Kolmogorov-Smirnov test. Results: Age at onset distributions were not significantly different between bipolar I and bipolar II patients. Severity was significantly higher in bipolar I patients. Limitations: Age at onset may be subject to recall bias. Structured interview by a senior psychiatrist, standard criteria for onset, family members or close friends supplementing information, same data collection and ascertainment procedures may have reduced bias. Conclusions.. Lack of significant difference in age at onset does not support the separation of the two disorders. Bipolar II disorder may be a less severe variant of bipolar disorder. (C) 1999 Elsevier Science B.V. All rights reserved.