Bipolar disease is a disorder of mood consisting of prolonged episodes of depression, interrupted by, or coexistent with episodes of mania. It was given the name manic-depressive disease by Kraepelin in 1896, and it was with him that our current clinical concept of this disorder originated. He viewed the manic and depressive attacks as opposite poles of the same underlying process and pointed out that, unlike dementia praecox (the prevalent name at the time, given by Pick, for schizophrenia), bipolar psychosis entails no intellectual deterioration. A traditional view of this disease was that of a periodic or cyclic condition in which one major mood swing was followed by an equal but opposite excursion. This is seldom the case, however. Episodes of depression are more than twice as frequent as manic ones, and according to current experts, the most common form of the illness is characterized by episodic depression alone with many patients having several episodes of depression before their first period of mania.
Recurrence of episodes of pure mania without interspersed episodes of depression is known but relatively less common. As a consequence, bipolar psychosis has been divided into two subtypes: the unipolar group, in which only an endogenous depressive illness occurs, and a bipolar group, in which one or more bouts of mania occur with or without depression. The bipolar variety occurs in approximately 10 percent of patients with affective disorder. The biologic accuracy of this classification has not been critically determined. There has been an arbitrary further subdivision of bipolar I to denote at least one episode of full mania, and bipolar II when the process entails an episode of hypomania.
In addition, there are mixed affective states, in which symptoms of both depression and mania occur within a single episode of the illness. A so-called “rapid-cycling” form of bipolar disease has also been recognized in which four or more circumscribed cycles of manias and depression occur in a year. Like other variants of the disease, it tends to have an aberrant or unpredictable response to medication. Still other patients with affective elements of depression present with atypical features; for example, instead of anorexia, weight loss, and insomnia, they sleep and eat excessively.
The prevalence of bipolar disease cannot be stated with precision, mainly because of varying criteria used for diagnosis. Certainly depression and depressive episodes are ubiquitous and mania is less common. The apparent increase of the disease in the past 50 years probably reflects a growing awareness of the condition among both physicians and the laity. Studies of large groups of patients from relatively isolated areas of Iceland and the Danish islands of Bornholm and SamsØ indicated that 5 percent of men and 9 percent of women developed symptoms of major depression, mania, or both at some time during their lives (Goodwin and Guze). More recent studies, such as the one conducted by the National Comorbidity Survey, report lifetime prevalence for bipolar disorder in the United States as 4.5 percent (Merikangas et al). According to the Global Burden of Disease Study, the incidence of bipolar disease increased by about 50 percent between 1990 and 2013 but it is still considered rare by comparison to depression and to other medical diseases (Ferrari).
Bipolar disease occurs most frequently in middle and later adult years, with a peak age of onset between 55 and 65 for both sexes. However, a significant proportion of patients experience the first attack in childhood, adolescence, or early adult life. Depression is also a major problem in the elderly. Blazer and Williams, who studied 997 persons older than age 65 years in North Carolina, found symptoms of a major depressive illness in 3.7 percent. The disease was 2 or 3 times more frequent among women. There is no known explanation for this gender difference, but some have speculated that just as many men are depressed, only they deny it or turn to alcohol. Patients in the bipolar group have an earlier age of onset, more frequent and shorter cycles of illness, and a greater prevalence of affective disorder among their relatives than do patients with unipolar depression (Winokur).