The presence of depression is necessary for such a diagnosis. In most cases of Bipolar II disorder, the predominant symptom is major depression and the episodes of hypomania may be much milder and relatively brief. Bipolar II disorder is tricky to diagnose, especially in those cases where prolonged and chronic depression is present. When patients have been depressed for long periods of time and then feel better, they often report feeling extremely well, which is in contrast to when they were depressed. Distinguishing these feelings of well being from states of mild euphoria or hypomania is often quite difficult.
Cyclothymic disorder is another variant of manic depressive illness.
It is characterized by chronic fluctuations in mood between periods of hypomania and periods characterized by mild depressive symptoms. The hypomanic periods are mild, and are never severe enough to reach full criteria for a manic episode. Also, the depressive periods are relatively mild and there are not sufficient symptoms to qualify for the diagnosis of major depressive disorder. The illness is usually persistent and chronic. Because of the mood fluctuations and the associated symptoms of either hypomania or depression, these patients can appear to be unstable, inconsistent and dysfunctional and the diagnosis may be missed.