Saturday, December 9, 2023
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High-frequency recurrence of mood episodes has been noted in the medical literature for at least 100 years.[1] The term rapid cycling was coined in 1974, when Dunner and Fieve[2] described a group of lithium-unresponsive manic-depressive patients who were noted to have at least 4 episodes of mania and/or depression per year. This general definition was later validated and then incorporated into the DSM-IV, which includes rapid cycling as a course specifier for bipolar disorder.[3] In DSM-IV, rapid cycling is defined by at least 4 mood episodes (mania, hypomania, depression, or mixed) that occur during the year prior to diagnosis. Each episode must be followed by return to euthymia for at least 2 months, or by a switch in mood polarity. Estimates of the point-prevalence of rapid cycling among bipolar patients are 10% to 20% among clinical samples.[3] "Looser" definitions involving monthly (ultrarapid) or weekly-daily (ultra-ultra-rapid) cycling have been described by both clinicians and investigators, although the diagnostic validity of such constructs remains controversial.
Rapid cycling clearly appears more frequently in females and seems to be associated with hypothyroidism and bipolar II disorder.[1,4] (Bipolar II disorder includes hypomanic and depressive episodes in the absence of mania, while bipolar I disorder is characterized by manic episodes.) Other features purported to differentiate rapid-cycling from non-rapid-cycling patients include earlier onset of illness, longer duration of illness, stronger family history of mood disorders, greater exposure to antidepressants,[1,4] and poorer global functioning.[4]
One of the key unresolved questions about rapid cycling is whether it should be considered a transient phenomenon, a distinct and persistent bipolar subtype, or an evolutionary outgrowth of repeated episodes of illness. Studies of the natural history of rapid cycling provide conflicting evidence. In a longitudinal study from Coryell and colleagues[5] of 39 rapid-cycling patients followed for 5 years, only 1 remained in a rapid-cycling state for the entire time. By contrast, Koukopoulos and colleagues'[6] naturalistic study of 109 rapid-cycling clinic patients showed that over half still met criteria for rapid cycling at the end of a follow-up period that ranged from 2 to 36 years.
