The diagnosis of major depression is made when the patient presents with the necessary signs and symptoms of a major depressive episode. The diagnostic category of major depression represents the unipolar form of the major affective disorders, in which patients manifest only the single pole of affect, that of depression. The diagnosis of recurrent major depression is made when major depressive episodes are repeated throughout a patient’s lifetime and is synonymous with the term recurrent unipolar depression. Following the first episode, between 50 and 80 percent of patients will have at least one more major depressive episode. Approximately 10 to 15 percent will have a subsequent manic episode, at which point the patient is then reclassified as having a bipolar disorder. Major depression is approximately twice as common in women as men. The point prevalence in the adult population ranges from 4.5 to 9.3 percent for women and 3.2 percent for men. The peak onset for first episodes in women is from 35 to 45 years; it decreases with age until 55, when the risk increases. The risk for younger men is lower but appears to increase steadily with age. Most natural-course studies indicate that unipolar patients average two to three major depressive episodes during their lifetimes, although some patients have only single episodes and others have many more. The average duration of an untreated depressive episode is 8 to 9 months with a range of 5 to 13 months. There is no established relationship between risk for major depression and socioeconomic class, race, education, or occupation.
Not all clinically significant depressive phenomena present as classic major depressions. The diagnostic categories of dysthymic disorder and atypical depression are clinical manifestations of depression without the full features of a major affective disorder. There is a high degree of heterogeneity and overlap between these two diagnostic categories. Patients who have some of the signs and symptoms of a depressive episode and who feel chronically dysphoric but do not meet full criteria for major depression are categorized here. Continued research has gradually identified a more homogeneous patient population with atypical features. Patients with atypical depression may have initial insomnia rather than early morning awakening and often may be hypersomniac. Their mood is frequently worse in the evening rather than the morning, and they also complain of a generalized dysphoria combined with fatigue, low energy, irritability, tension, and anxiety. Rather than being unreactive to environmental changes, as is usually seen in major depressive episodes, they often can be temporarily cheered up by specific environmental changes. Further, they are often not anorexic and may be hyperphagic and crave carbohydrates. Some experts have suggested that patients with atypical depression should be classified in a new diagnostic category entitled mood reactive depression.