The American Psychiatric Association publishes the Diagnostic and Statistical Manual of Mental Disorders (DSM), which describes the criteria necessary for the diagnosis of all mental disorders, including Major Depression. In the DSM, Major Depression appears as a member of the Depressive Disorders category, which also includes the Bipolar Disorders, Dysthymic Disorder, Cyclothymia and Depressive Disorder Not Otherwise Specified. These various mood disorders are all similar in that they all have something to do with disordered mood, and more specifically, with depressed mood. They are distinguished by the extent and severity of a person's mood disturbance, and by the direction (up or down) of the moods involved.
Here is a key point: The mood disorder diagnoses are essentially defined as patterns of mood disturbances observed through time. Clinicians choose from among the various mood-related diagnoses on the basis of their observation of patients' sequence of mood episodes. Most people with mood disorders will have (or have already had) a history of multiple mood episodes. Individual mood episodes last for several weeks or months and then give way to normal mood, or to another mood episode.
In order to fully understand how mood disorders are defined, you first have to understand the concept of mood episodes. There are four kinds of mood episodes described in the DSM: Major Depressive, Manic, Hypomanic, and Mixed. Major Depressive episodes are characterized by the classic symptoms described above. Manic episodes are characterized by a persistently elevated, expansive, or irritable mood, lasting at least 1 week (or any duration if hospitalization is necessary). In addition, three (or more) of the following symptoms must be present (four symptoms must be present if the person's mood is only irritable):
- Inflated self-esteem or grandiosity
- Decreased need for sleep (e.g., feels rested after only 3 hours of sleep)
- More talkative than usual or pressure to keep talking
- Racing thoughts
- Distractibility (i.e., attention too easily drawn to unimportant or irrelevant external stimuli)
- Increase in goal-directed activity (either socially, at work or school, or sexually) or feelings of agitation/restlessness
- Excessive involvement in risky activities (e.g., shopping sprees, sexual indiscretions, or foolish business investments)
Hypomanic episodes are a milder form of manic episodes. Both share the same list of symptoms described above. However, the DSM criteria for Hypomanic episodes state that the person's mood disturbance occurs throughout at least 4 days (rather than 1 week as with a Manic Episode).
Mixed episodes are essentially a combination of manic and depressive episodes that become superimposed so that symptoms of both are present (at different times) during the same day. More specifically, the criteria are met both for a Manic Episode and for a Major Depressive Episode nearly every day during at least a 1-week period.
Major Depression is a distinct and separate condition from Bipolar Disorder and the other mood disorders. By definition, people diagnosed with Major Depression show only a history of one or more major depressive episodes. People with Major Depression never have a history of manic or mixed episodes, and neither do they show signs of hypomania. People with Major Depression also have relatively severe mood symptoms. People who show signs of depressive mood on a regular basis but who do not meet the formal criteria for a depressive mood episode cannot be diagnosed with Major Depression. Such individuals will instead tend to have some other mood diagnosis, such as Dysthymic Disorder.
In this article, we focus on the Unipolar forms of depression; namely Major Depressive Disorder, Dysthymic Disorder, and Depressive Disorder Not Otherwise Specified. The other mood disorders tend to be variations on the theme of bipolar disorder and are discussed in our Bipolar Disorders Topic Center. Throughout our discussion it is important to keep in mind that the term "depression" is not particularly specific. There are multiple kinds of depression; and the diagnosis of a particular disorder varies depending on the severity, duration, and persistence of symptoms.