Am ] Psychiatry 1 52:3, March 1995 385 Long-Term Stability of Polarity Distinctions in the Affective Disorders William Coryell, M.D., Jean Endicott, Ph.D., Jack D. Maser, Ph.D., Martin B. Keller, M.D., Andrew C. Leon, Ph.D., and Hagop S. Akiskal, M.D. Objective: This analysis aimed to quantify the long-term stability of distinctions between nonbipolar, bipolar II, and bipolar I affective disorders and to determine the predictors of shifts in patients’ diagnoses among these categories. Method: Probands entered the study as they sought treatment for manic, major depressive, or schizoaffective disorder diagnosed ac- cording to the Research Diagnostic Criteria. After thorough baseline evaluations, 605 patients with nonbipolar major depressive disorder or schizoaffective disorder, depressed type; 96 with bipolar II disorder; and 231 with bipolar I disorder or schizoaffective disorder, manic type, began the follow-up study. Direct interviews took place at 6-month intervals for the first S years andannually thereafter. Results: Only 20 (5.2%) ofthe 381 initially nonbipo- lar probands who completed 10 years of follow-up developed mania during that time, and only 19 (5.0%) developed hypomania. A slightly higher proportion ofthe 67 who began with bipolar II disorder developed mania during the 10 years. Although 1 01 (66.4%) of the 152 bipolar I or schizoaffective manic probands developed subsequent manic episodes, only 11 (7.2%) developed hypomanic episodes and no mania. Young age at intake and at onset and chronicity of the index episode predicted shifts from nonbipolar to bipolar II disorder. Psy- chosis and a family history of mania predicted shifts from nonbipolar to bipolar I disorder. Conclusions: The high stability of baseline distinctions between nonbipolar, bipolar II, and bipolar I disorders, in combination with previously described family study data, strongly sup- ports the separation of these disorders for both clinical and research purposes. (AmJ Psychiatry 1995; 152:385-390) E vidence of several sorts supports a distinction be- tween depressed patients with a history of hypo- mania (bipolar II disorder) and depressed patients who have had neither mania nor hypomania (nonbipotar disorder). Depressive symptoms among the former are more likely to include features characteristic of bipolar I depression-hypensomnia, hyperphagia, psychomo- ton retardation, and delusions ( 1 ) Patients with bipolar II disorder have a higher frequency of episodes than do those with nonbipotar disorder, and in this they also resemble patients with bipolar I disorder (2, 3). Fur- thenmone, bipolar II disorder appears to be familial: the relatives of bipolar II probands have substantially higher rates of bipolar II disorder than do the relatives of nonbipotan probands (4, 5). Despite the similarities between bipolar II and bipolar I disorders, the data also separate these two conditions. Received Oct. 1 9, 1 993; revision received Sept. 6, 1 994; accepted Sept. 28, 1994. From the NIMH Collaborative Program on the Psy- chobiology of Depression-Clinical Studies. Address reprint requests to Dr. Coryell, Department of Psychiatry, University of Iowa Hospi- tals and Clinics, 200 Hawkins Dr., Iowa City, IA 52242. First, the distinction appears to be stable over time. Bi- polar II patients were only slightly more likely than nonbipolan patients, and much less likely than bipolar I patients, to develop manic episodes during a S-year follow-up (2). Second, rates of bipolar II disorder are substantially elevated among the relatives of bipolar II probands but not among the relatives of bipolar I pro- bands (4). These findings converge to recommend the study of bipolar II disorder apart from both nonbipolar and bi- polar I conditions. However, two factors make confi- dence in diagnosis a particular concern in such studies. Phenomenologicalty, hypomania shades into mania. The boundaries used in current interview schedules were not empirically derived and depend on the number of manic symptoms, the duration of those symptoms, and the degree of resulting impairment. Moreover, per- sons with bipolar II disorder are much more likely to present themselves for treatment during depressive epi- sodes than during hypomanic phases. Consequently, the distinction between nonbipotar and bipolar II dis- orders is typically based on retrospective accounts, and this may limit reliability (6).