Manic Depressive Illnesses
According to the Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV), there are four types of bipolar disorder, differing primarily in symptom severity and the length of time between manic and depressive episodes.
Bipolar type I is the most severe and potentially dangerous form of the illness, capable of causing great difficulty in daily activities and relationships. It is characterized by manic or mixed episodes that last at least seven days or by manic symptoms that are so severe that the person needs emergency hospital care.
Manic or mixed episodes are followed by episodes of major depression that last weeks or even years. Fortunately, many people with bipolar I disorder experience long symptom-free periods.
Bipolar type II involves alternating hypomanic (lasting at least four days) and depressive episodes but no full-blown manic or mixed episodes. While "up" periods are marked by milder symptoms, depressive episodes may be severe and debilitating.
Generally, people with bipolar type II can function in their normal daily routine while hypomanic and might simply seem to be extremely cheerful, sociable, or "the life of the party." During the depressive phase, the level of functioning varies significantly among individuals. Typically, an episode of significant depression follows soon after hypomania. Rapid cycling of moods is more likely to occur with bipolar II than with bipolar I.
Cyclothymia is an even more mild form of mood cycling with highs and lows that continue for at least two years but never reach the severity of major depression or mania. This can make it hard to distinguish from normal variations in mood and personality. In most people, the pattern is irregular and unpredictable, and hypomania or depression can last for days or weeks. In between up and down moods, a person might have normal moods for more than a month.
Bipolar disorder not otherwise specified (BP-NOS) is diagnosed when symptoms don't meet the criteria for bipolar I or II or cyclothymia. Symptoms may not last long enough, or the person may have too few of them. But the symptoms are clearly out of the person's normal range of behavior.