Atypical depression (AD) is a subtype of dysthymia and major depression, sharing many of the symptoms of both, but also being characterized by mood reactivity—being able to experience improved mood in response to positive events. In contrast, sufferers of "melancholic" depression generally cannot experience positive moods, even when good things happen. Additionally, atypical depression is characterized by reversed vegetative symptoms, namely over-eating and over-sleeping, and separately by interpersonal rejection sensitivity.

"Hysteroid dysphoria" has been described in outpatient populations and is thought to be a subtype of atypical depression involving rejection sensitivity and therapeutic response to monoamine oxidase inhibitors.^[1]

Despite its name, "atypical" depression is actually the most common subtype of depression^[2][3]—up to 40% of the depressed population may be classified as having atypical depression.

  Symptoms

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.

c) Criteria are not met for Melancholic Depression or Catatonic Depression during the same episode.

  Research

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 other psychiatric syndromes such as panic disorder, social phobia, avoidant personality disorder, or body dysmorphic disorder.^{[citation needed]}

Recent research suggests that females are more likely to be affected by atypical depression than males, and that young people are more likely to suffer from hypersomnia while older people are more likely to suffer from polyphagia.^[4]

Medication response differs between chronic atypical depression and acute melancholic depression. Some studies^[5] suggest that an older class of drugs, the monoamine oxidase inhibitors (MAOIs), may be more effective at treating atypical depression. While the more modern SSRIs are usually quite effective in this illness, the tricyclic antidepressants typically are not.^{[citation needed]}

In addition, SSRI responses can often be enhanced with "booster" medications, and medication regimens seem to work best when combined with appropriate psychotherapy.^[6] It is important to remember that such co-morbid syndromes as panic disorder may not be fully treated without additional medication(s).

It has been noted that patients with atypical depression often suffer from intense cravings for carbohydrates. A mineral supplement, chromium picolinate, was found to assuage these cravings.^[7][8] It also was found to have an antidepressant effect on some atypical depression sufferers.^[8]

Some hypothesize that atypical depression may be related to thyroid dysregulation. Some studies have found subtle thyroid abnormalities in people with atypical depression.^[9] Another study suggests that patients may benefit from triiodothyronine, a medication used to treat hypothyroidism.^[10]

  References

  Additional resources

1. Atypical Depression Actually Very Typical
2. 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. http://linkinghub.elsevier.com/retrieve/pii/S0165-0327(05)00015-7. 
3. Atypical Depression - Dr. Ivan Goldberg's "Depression Central"