Objective: To propose terminology to distinguish cycles from episodes in children and adults with bipolar disorder (BP).
Methods: To examine current definitions of rapid cycling and episodes in both child and adult BP, an Internet search of the MEDLINE database was conducted.
Results: Investigations of rapid cycling in adults used the terms cycle and episode interchangeably to describe discrete periods of mood disorders. Two studies of children and one study of adults with BP, however, reported cycles occurring daily (ultradian cycling) or every few days (ultrarapid cycling). Without definitions to differentiate cycles from episodes, determining the overall duration of illness in subjects who experience ultrarapid or ultradian cycling is not possible. For example, a child cycled twice a day, every day, for 365 days (1 year). With the terminology currently in use, it is unclear whether this should be described as a single episode that had a duration of 365 days or as approximately 730 episodes (2 cycles per day x 365 days), each less than 24 hours in duration. Moreover, adults with BP may have more intermittent pathology than children (e.g., adults may cycle 4 days per week, versus children may cycle 7 days per week).
Conclusion: The following definitions are proposed. (1) Episodes will be defined by (a) the duration from onset to offset of a period of at least 2 weeks in length during which only one mood state persists or (b) the duration from onset to offset of a period of ultrarapid or ultradian cycling for at least 2 weeks. (2) Cycles will be defined by mood switches occurring daily or every few days during an episode. Further research will be needed to elucidate potential differences between child and adult cycling patterns.