ABSTRACT
In 1974, Dunner and Fieve described a variant of bipolar disorder marked by extensive mood fluctuations, giving rise to the concept of rapid cycling (1). Now incorporated into our current diagnostic nomenclature, rapid cycling is defined by the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th Edition) as the occurrence of four or more mood episodes during a 12-month period, inclusive of mixed episodes, mania, hypomania, or major depression. Over the past 30 years, rapid cycling as a modifier of the course of bipolar disorder has been substantiated by differences in gender, bipolar subtype, propensity for thyroid dysfunction, and prospectively defined outcomes (2-6). It is now recognized that patients with rapid cycling must contend with an earlier age of mood disorder onset, a higher lifetime number of mood episodes, and greater mood episode severity (2). In fact, compared with their non-rapid-cycling counterparts, patients with rapid-cycling experience eight times more depressive and nine times more hypomanic/manic episodes over a 12-month period (4).
