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There is no clear consensus as to how many types of bipolar disorder exist. In DSM-IV-TR and ICD-10, bipolar disorder is conceptualized as a spectrum of disorders occurring on a continuum. The DSM-IV-TR lists four types of mood disorders which fit into the bipolar categories: Bipolar I, Bipolar II, Cyclothymia, and Bipolar Disorder NOS (Not Otherwise Specified).


Bipolar I
In Bipolar I disorder, an individual has experienced one or more manic episodes with or without major depressive episodes. For a diagnosis of Bipolar I disorder according to the DSM-IV-TR, one or more manic or mixed episodes are required. A depressive episode is not required for the diagnosis of Bipolar I but it frequently occurs.


Bipolar II
Bipolar II disorder is characterized by hypomanic episodes rather than actual manic episodes, as well as at least one major depressive episode. Patients with a Bipolar II diagnosis under the DSM IV criteria cannot, by definition, ever have had a manic episode prior to their diagnosis. However, a Bipolar II diagnosis is not a guarantee that they will not eventually suffer from such an episode in the future.[citation needed]

Hypomanic episodes do not go to the full extremes of mania (i.e. do not usually cause severe social or occupational impairment, and without psychosis), and this can make Bipolar II more difficult to diagnose, since the hypomanic episodes may simply appear as a period of successful high productivity and is reported less frequently than a distressing, crippling depression. For both Bipolar I and II, there are a number of specifiers that indicate the presentation and course of the disorder, including "chronic", "rapid cycling", "catatonic" and "melancholic".


Cyclothymia
Cyclothymia involves a presence or history of hypomanic episodes with periods of depression that do not meet criteria for major depressive episodes. 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.


Bipolar NOS
Bipolar Disorder NOS, sometimes called "sub-threshold" Bipolar Disorder, is a "catch-all" diagnosis that is used to indicate bipolar illness that does not fit into any of the formal DSM-IV bipolar diagnostic categories (Bipolar I, Bipolar II, or cyclothymia). If an individual seems to be suffering from bipolar spectrum symptoms (e.g. some manic and depressive symptoms) but does not meet the criteria for one of the subtypes mentioned above, he or she receives a diagnosis of Bipolar Disorder NOS (Not Otherwise Specified). Despite not fully meeting one of the formal diagnostic categories, Bipolar NOS can still significantly impair and adversely affect the quality of life of the patient.

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Wasteland said:

Known four.
One really well.

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