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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:
- Significant weight gain or increase in appetite;
- Hypersomnia (sleeping too much, as opposed to the insomnia present in melancholic depression);
- Leaden paralysis (i.e., heavy, leaden feelings in arms or legs);
- Long-standing pattern of interpersonal rejection sensitivity (not limited to episodes of mood disturbance) that results in significant social or occupational impairment.
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.
- American Psychiatric Association. (2000). Mood Disorders. In Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.) Washington, DC: Author.
- "Atypical depression". Mayo Clinic. Retrieved 2013-06-23.
- Posternak, Michael; Zimmerman,M. (November 2001). "Symptoms of Atypical Depression". Psychiatry Research 104 (2): 175–181. doi:10.1016/S0165-1781(01)00301-8. PMID 11711170. Retrieved 28 November 2011.
- http://www.mayoclinic.com/health/atypical-depression/AN01363 Atypical depression: How is it different from 'regular' depression?
- Vaishnavi, S.; Gadde K; Alamy S; Zhang W; Connor K; Davidson JR. (2006). "Modafinil for atypical depression: effects of open-label and double-blind discontinuation treatment.". Journal of Clinical Psychopharmacology 26 (5): 523. doi:10.1097/01.jcp.0000227700.263.75.39. PMID 16855454.
- http://www.workpsychcorp.com/newsweek2.html Depression Update: Atypical Depression
- http://web.archive.org/web/20070317050218/http://www.webmd.com/depression/news/20040315/atypical-depression-thyroid-link-still-alive Atypical Depression: Thyroid Link Still Alive
- Iosifescu DV, Nierenberg AA, Mischoulon D, et al. (August 2005). "An open study of triiodothyronine augmentation of selective serotonin reuptake inhibitors in treatment-resistant major depressive disorder". J Clin Psychiatry 66 (8): 1038–42. doi:10.4088/JCP.v66n0812. PMID 16086620.
- Atypical Depression Actually Very Typical
- Stewart JW, Quitkin FM, McGrath PJ, Klein DF (June 2005). "Defining the boundaries of atypical depression: evidence from the HPA axis supports course of illness distinctions". J Affect Disord 86 (2–3): 161–7. doi:10.1016/j.jad.2005.01.009. PMID 15935235.
- Atypical Depression - Dr. Ivan Goldberg's "Depression Central"