Bipolar disorder, also known as manic depressive illness, is a serious, double-edged mental illness. In contrast to the sustained bleakness of major depression (technically called unipolar disorder when episodes only involve major depression and no manic or hypomanic periods), bipolar disorder is characterized by cyclical periods of high energy and elation and then low energy and despair. The pattern of the mood alternations varies widely among those with the disorder. In some people, years of normal functioning can separate manic and depressive episodes. In others, the episodes cycle frequently, three, four, or more times a year, with respites in between. For some people, depression and mania cycle continuously. There are also people who experience episodes with mixed features, in which symptoms of mania and depression occur together or alternate rapidly within a brief period of time. And for a rare few, an episode of bipolar disorder may occur only once in a lifetime. If an episode occurs twice, it is usually followed by others. Generally, the depressive phase lasts longer than the manic phase. It also tends to be more frequent. The cycle can be erratic.
Bipolar disorder is known to affect about 2.6% of U.S. adults in any given year, although its frequency may be somewhat higher because cases go untreated or misdiagnosed. Men and women are equally susceptible. Much evidence suggests that the illness has at least a partial genetic basis, but its origins are still uncertain. The symptoms are thought to result from abnormal functioning of brain circuits that regulate mood, thinking, and behavior and are beyond voluntary control. The disorder is not only life-disrupting but can also be dangerous. As many as 10% to 15% of people with bipolar disorder commit suicide, usually when they are in the midst of a severe depression and may feel particularly hopeless about the future.
Fortunately, great strides have recently been made in treating this illness. In most cases, the symptoms can be controlled effectively by medication and other therapies.
The disorder occurs in two main forms, known as bipolar I and bipolar II. They may have separate genetic origins. In bipolar I, both phases of the illness are apt to be very pronounced. In bipolar II, mania is often mild (it is termed hypomania), and the depression can be either mild or severe. Bipolar II is more difficult to diagnose and is often mistaken for unipolar or major depressive disorder. It has fewer and shorter periods of remission than bipolar I, tends to be more common in women, and is somewhat less responsive to treatment. It may be the more common form of bipolar disorder.
The illness is sometimes linked to seasonal affective disorder, with depression occurring in late fall or winter, giving way to remission in the spring, and progressing to mania or hypomania in the summer.
About one in five cases of bipolar disorder begins in late childhood or adolescence, referred to as early-onset bipolar disorder. Adolescents are more likely than adults to have more frequent mood swings, mixed episodes, and relapses, and they are more apt to be misdiagnosed. Usually, however, the illness strikes during early adulthood and the average onset is before age 25. The first episode in males is likely to be manic. The first episode in females is typically depressive (and frequently, a woman will experience several episodes of depression before a manic episode occurs). As patients grow older, recurrences of either bipolar I or bipolar II tend to come more frequently and last longer.
Bipolar disorder is thought to result from abnormal functioning of certain brain circuits, which may in part be related to abnormal functioning of genes. Possible chemical abnormalities related to brain circuit dysfunction are not fully understood, but may be related to serotonin, norepinephrine, dopamine, glutamate, and gamma-aminobutyric acid (GABA), among others. The likelihood that genes play a role is supported by the fact that there is sometimes a family history of recurrent mood disorders or suicide.