Recognizing the diversity of types and intensities of mood episodes, the DSM-IV-TR (the Diagnostic and Statistical Manual of Mental Disorders, the book that describes mental health diagnoses) has subdivided the diagnosis of bipolar disorder into four basic categories, each defined by a particular pattern of severity of spontaneous depressions, manias, hypomanias or mixed episodes. The term "Bipolar I Disorder" is applied to patients who demonstrate full-strength manic and depressive episodes. The term "Bipolar II Disorder" is applied to patients who demonstrate full-strength depression, but only hypomanic presentations rather than full-strength manias. The term "Cyclothymic Disorder" is used to describe patients who demonstrate repeated mood swings which are never quite severe enough to qualify as major depressive or manic episodes. Finally, the term "Bipolar Disorder, Not Otherwise Specified (NOS)" is used to describe all other patients with bipolar symptoms which cannot neatly be fitted into the above categories. We'll have more to say about DSM bipolar diagnoses in our discussion below.
Periodicity of Swings
Besides the energy or intensity of mood episodes, the other important factor relating to bipolar mood swings has to do with their periodicity; how long each episode lasts, and how rapidly they fluctuate. Most of the time bipolar mood swings occur with relative slowness, over periods of weeks and months. Usually, less than four complete mood cycles occur within a given year, and each mood episode might last up to two months.
There is generally a period of relatively normal mood that occurs between mood episode extremes. However, some individuals bipolar disorder do not experience this normal inter-episode period and instead experience this interval as a point in time when their mood symptoms are milder than normal (rather than being absent). For example, a person who is clearly between episodes might still feel low on some days or slightly manic on others.
Though less common than the longer cycling forms of bipolar disorder, a rapid-cycling variation of bipolar disorder is recognized. Rapid cycling bipolar disorder occurs when complete mood cycle periods occur four or more times per year. Rapid cycling bipolar conditions are thought to occur in 20% or less of all bipolar patients.
Two additional cycling terms are now beginning to enter the literature. Ultra-rapid cycling is in use to describe cases where complete mood cycles occur in less than one month. Ultridian cycling is in use to indicate cases where complete mood cycles occur inside the space of one day (and thus might be confused with a mixed episode). It is important to note that ultra-rapid and ultridian forms of mood cycling are not yet formally recognized in the DSM and thus are not currently official terms.
Rapid cycling in any form of bipolar disorder tends to be associated with a poorer long-term prognosis, which is to say, rapid-cyclers don't tend to hold their lives together as well as do bipolar patients who have longer cycles.