Flux is the fundamental nature of bipolar disorder. Both within and between individuals with the illness, energy, mood, thought, sleep, and activity are among the continually changing biological markers of the disorder. The diagnostic subtypes of bipolar disorder are thus static descriptions--snapshots, perhaps--of an illness in continual change. Individuals may stay in one subtype, or change into another, over the course of their illness. The DSM V, to be published in 2011, will likely include further and more accurate sub typing
There are currently four types of bipolar illness. The DSM-IV-TR details four categories of bipolar disorder, Bipolar I, Bipolar II, Cyclothymia, and Bipolar Disorder NOS (Not Otherwise Specified).
According to the DSM-IV-TR, a diagnosis of Bipolar I disorder requires one or more manic or mixed episodes. A depressive episode is not required for a diagnosis of BP I disorder, although the overwhelming majority of people with BP I suffer from them as well.
Bipolar II, the more common but by no means less severe type of the disorder, is usually characterized by one or more episodes of hypomania and one or more severe depressions. A diagnosis of bipolar II disorder requires only one hypomanic episode. This stipulation is used mainly to differentiate it from unipolar depression. Although a patient may be depressed, it is very important to find out from the patient or the patient's family or friends if hypomania has ever been present, using careful questioning. This, again, avoids the antidepressant problem. Recent screening tools such as the Hypomanic Check List Questionnaire (HCL-32) have been developed to assist the quite often difficult detection of Bipolar II disorders.
A diagnosis of Cyclothymic Disorder requires the presence of numerous hypomanic episodes, intermingled with depressive episodes that do not meet full criteria for major depressive episodes. The main idea here is that there is a low-grade cycling of mood which appears to the observer as a personality trait, but interferes with functioning.
If an individual clearly seems to be suffering from some type of bipolar disorder but does not meet the criteria for one of the subtypes above, he or she receives a diagnosis of Bipolar Disorder NOS (Not Otherwise Specified).