Atypical depression can be a "specifier" for either major depression or dysthymic disorder. People with atypical depression have often experienced depression first at an early age, during their teenage years.
A person with classic major depression has at least five of the following nine symptoms:
Sadness or depressed mood most of the day or almost every day
Loss of enjoyment in things that were once pleasurable
Major change in weight (gain or loss of more than 5% of weight within a month) or appetite
Feelings of hopelessness or worthlessness or excessive guilt almost every day
Problems with concentration or making decisions almost every day
Recurring thoughts of death or suicide, suicide plan, or suicide attempt
Dysthymic disorder is a condition involving the presence of a depressed mood more days than not for at least a two year period in adults (one year in children and adolescents) plus at least two of the above associated symptoms, but fewer than the five symptoms which define a major depressive episode.
Despite its name, atypical depression is very common. It is contrasted with "melancholic" depression, another subtype of depression, involving symptoms of insomnia (rather than oversleeping), loss of appetite (rather than increased appetite), a relative lack of mood reactiveness to environmental circumstances, and a markedly diminished ability to feel pleasure.
What are the symptoms of atypical depression?
The main characteristic of atypical depression that distinguishes it from melancholic depression is mood reactivity. In other words, the person with atypical depression will see his or her mood improve if something positive happens. In melancholic depression, positive changes will seldom bring on a change in mood. In addition, diagnostic criteria call for at least two of the following symptoms to accompany the mood reactivity:
Sleeping too much (hypersomnia)
Increased appetite or weight gain
Having a more intense reaction or increased sensitivity to rejection, resulting in problems with social and work relationships
Having a feeling of being weighed down, paralyzed, or "leaden"
A doctor will investigate physical causes for any of these symptoms. That will include a physical exam and tests to look for a problem such as hypothyroidism. With hypothyroidism, having low levels of thyroid hormone can lead to symptoms that include depression and weight gain.