Thorough evaluation of many persons with depression reveals bipolar traits, and as many as one in five patients with a depressive disorder also develops frank hypomania or mania. Most switches from unipolar to bipolar disorder occur within 5 yr of the onset of depressive manifestations. Predictors of a switch include early onset of depression (< 25 yr old), postpartum depression, frequent episodes of depression, quick brightening of mood with somatic treatments (eg, antidepressants, phototherapy, sleep deprivation, electroconvulsive therapy), and a family history of mood disorders for three consecutive generations.
Between episodes, patients with bipolar disorder exhibit depressive moodiness and sometimes high-energy activity; disruption in developmental and social functioning is more common than in unipolar disorder. In bipolar disorder, episodes are shorter (3 to 6 mo), age of onset is younger, onset of episodes is more abrupt, and cycles (time from onset of one episode to that of the next) are shorter than in unipolar disorder. Cyclicity is particularly accentuated in rapid-cycling forms of bipolar disorder (usually defined as >= 4 episodes/yr).
In bipolar I disorder, full-fledged manic and major depressive episodes alternate. Bipolar I disorder commonly begins with depression and is characterized by at least one manic or excited period during its course. The depressive phase can be an immediate prelude or aftermath of mania, or depression and mania can be separated by months or years.
In bipolar II disorder, depressive episodes alternate with hypomanias (relatively mild, nonpsychotic periods of usually < 1 wk). During the hypomanic period, mood brightens, the need for sleep decreases, and psychomotor activity accelerates beyond the patient's usual level. Often, the switch is induced by circadian factors (eg, going to bed depressed and waking early in the morning in a hypomanic state). Hypersomnia and overeating are characteristic and may recur seasonally (eg, in autumn or winter); insomnia and poor appetite occur during the depressive phase. For some persons, hypomanic periods are adaptive because they are associated with high energy, confidence, and supernormal social functioning. Many patients who experience pleasant elevation of mood, usually at the end of a depression, do not report it unless specifically questioned. Skillful questioning may reveal morbid signs, such as excesses in spending, impulsive sexual escapades, and stimulant drug abuse. Such information is more likely to be provided by relatives.
Patients with major depressive episodes and a family history of bipolar disorders (unofficially called bipolar III) often exhibit subtle hypomanic tendencies; their temperament is termed hyperthymic (ie, driven, ambitious, and achievement-oriented).
