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|Classification and external resources|
|Classification and external resources|
Atypical depression, or depression with atypical features as it has been known in the DSM, is depression that shares many of the typical symptoms of the psychiatric syndromes major depression or dysthymia but is characterized by improved mood in response to positive events. In contrast, people with melancholic depression generally do not experience an improved mood in response to normally pleasurable events. Atypical depression also features significant weight gain or an increased appetite, hypersomnia, a heavy sensation in the limbs and interpersonal rejection sensitivity that results in significant social or occupational impairment.
Despite its name, "atypical" depression does not mean it is uncommon or unusual. The reason for its name is twofold: (1) it was identified with its "unique" symptoms subsequent to the identification of melancholic depression and (2) its responses to the two different classes of antidepressants that were available at the time were different from melancholic depression (i.e., MAOIs had clinically significant benefits for atypical depression, while tricyclics did not).
Atypical depression is two to three times more common in women than in men. Individuals with atypical features tend to report an earlier age of onset (e.g. while in high school) in their depressive episode, which also tend to be more chronic and only have partial remission between episodes. Younger individuals may be more likely to have atypical features, whereas, older individuals may more often have episodes with melancholic features.
Atypical depression is more common in individuals with bipolar I, bipolar II, and major depressive disorder, recurrent, with seasonal pattern (seasonal affective disorder). Depressive episodes in bipolar disorder tend to have atypical features, as does depression with seasonal patterns.
The DSM-IV-TR defines Atypical Depression as a subtype of Major Depressive Disorder with Atypical Features, characterized by:
a) Mood reactivity (i.e., mood brightens in response to actual or potential positive events)
b) At least two of the following:
In general, atypical depression tends to cause greater functional impairment than other forms of depression. Atypical depression is a chronic syndrome that tends to begin earlier in life than other forms of depression — usually beginning in the teenage years. Similarly, patients with atypical depression are more likely to suffer from personality disorders and anxiety disorders such as: Borderline Personality Disorder, Avoidant Personality Disorder, Generalized Anxiety Disorder, and Obsessive Compulsive Disorder.
Medication response differs between chronic atypical depression and acute melancholic depression. Some studies suggest that the older class of antidepressants, monoamine oxidase inhibitors (MAOIs), may be more effective at treating atypical depression. While the more modern SSRIs and SNRIs are usually quite effective in this illness, the tricyclic antidepressants typically are not. The wakefulness-promoting agent Modafinil has shown considerable effect in combating atypical depression, maintaining this effect even after discontinuation of treatment. 
In addition, antidepressant responses can often be enhanced with supplemental medications, such as Bupropion or the atypical antipsychotic, Aripiprazole, which creates a combination treatment, and are offered additional effectiveness combined with psychotherapy. It is important to remember that such co-morbid syndromes as panic disorder may not be fully treated without additional medication(s).
Some experts hypothesize that atypical depression may be related to thyroid dysregulation. Some studies have found subtle thyroid abnormalities in people with atypical depression. Another study suggests that patients may benefit from triiodothyronine, a medication used to treat hypothyroidism.