Bipolar Disorders: Mixed States, Rapid-Cycling, and Atypical Forms

27 Beyond major depression and euphoric maniaProlonged single episodes accompanied by intermittent fluctuations within themoodstate(i.e.,cyclingaboveorbelowbaselineduetochangesinmedicationdosesorlevels) are counted as one episode. For example, patients who have one long period ofmania followed by a short period of hypomania due to the transient use of neurolepticsor benzodiazepines, followed by a return to mania, are counted as having only oneepisode (Calabrese et al., 2000). DSM-IV applies ‘‘rapid cycling’’ only to bipolar I andbipolar II disorders in recognition of the reality that rapid cycling of unipolar depressionis extremely rare, and when it does occur, the family history is usually positive forbipolar disorder (Tay and Dunner, 1992; Kilzieh and Akiskal, 1999).As noted above, the cut-off of four episodes per year has been criticized for beingarbitrary. The key question, still unanswered, is whether cycle length distributesmore or less evenly across a spectrum, or if there is a true bimodal distributioninto two concrete (as opposed to arbitrary) subgroups – namely, rapid-cycling andnon-rapid-cycling (Goodwin and Jamison, 1990; Coryell et al., 1992). Anotherproblem regarding the definition of rapid cycling relates to the nature and durationof the interepisodic period, which varies widely among studies. Studies differ regardingits duration and level of symptoms (Kilzieh and Akiskal, 1999): some require partialor full remission for at least 2 months or a switch to an episode of opposite polarity,other researchers have set the duration of remission as low as 4 weeks, while stillothers require a period of euthymia as long as the proximate episodes. Theprevalence of rapid cycling in bipolar populations is also indeterminate because mostof the data come from studies mostly done at tertiary centers with a high proportion ofdifficult-to-treat patients (Kilzieh and Akiskal, 1999). No community-based studieshave been conducted, and the true prevalence of rapid cycling in an unselected bipolarpatient population remains unknown (Kilzieh and Akiskal, 1999). Another problemrelated to the estimation of the prevalence of rapid cycling is its longitudinal instability;that is, it often occurs intermittently during the course of illness (Coryell et al., 1992).Studies on the prevalence of rapid cycling in a clinical bipolar population rangefrom 24.2% (Tondo et al., 1998) down to 13.6% (Maj et al., 1994), with others inbetween: Coryell et al. (1992) 18.5%, Dunner and Fieve (1974) 20%, andKoukopoulos et al.(1980) 19%. A prevalence of rapid cycling with ‘‘approximately5–15% of people with bipolar disorders seen in mood disorder clinics’’ is cited.Higher prevalence rates than those noted above were reported by Cowdry et al.(1983) from the US National Institute of Mental Health (56%), but this probablyreflects the specialization of this major research center.The gender difference – on average, more than 70% of rapid cyclers are females –is the most extensively replicated finding in rapid cycling (Table 1.3).The meta-analysis of Tondo et al.(1998) showed that, although the majority ofrapid-cycling cases (72%) are women, rapid cycling occurred in less than 30% ofthe total female bipolar population.