A depressive disorder will involve "episodes", such as hypomanic, manic, mixed and major depressive episodes.
The major depressive episode is more a part or a description of part of the overall disorder rather than a disorder in its own right. The major depressive episode meets certain criterion, such as duration of the episode, with evidence of certain symptoms. Not all of the symptoms are required to be exhibited, though.
In diagnosis, five or more of the following must be exhibited for a minimum of two weeks. Plus, the symptom of depressed mood and lost of interest or pleasure must be present during that period.
For adults: a depressed mood every day, most of the day, nearly every day. Adolescents and children might show as irritable.
There is a clear loss or diminishing of interest and inability to gain pleasure from almost all activities, again for most of the day and nearly every day.
Changes in appetite: there might be significant changes in weight. 5% within a month is a significant change of weight from either increased or decreased appetite.
Insomnia and hypersomnia occur. Insomnia is an inability to sleep and hypersomnia is sleeping too much.
There are psychomotor problems: either agitated or sluggish action.
Fatigue and decline of energy is exhibited.
Feelings are abnormal: there are excessive feelings or worthlessness, hopelessness, excessive guilt, excessive failure.
Concentration and decisiveness are decreased. Concentration is difficult.
There are repeated thoughts of death, suicide thoughts, with our without specific details or plans.
The evidence of any situational factors, such as death of a loved one, trauma, loss of a job and other situations where depression is normal may or may not rule out a diagnosis of major depression.
If there is a single episode:the Major Depressive Episode cannot be better explained by other causes or disorders, or is not superimposed on other disorders, such as Schizophrenia and Delusional Disorder.
Also in the single episode and the recurrent episode: There can never be a Manic, Mixed or Hypomanic episode, unless there is a substance, treatment or general medical condition that induces the additional episodes and symptoms.
The recurrent Major Depressive Episode requires two or more episodes.
There are also factors of severity, psychosis, chronicity and remission. There may also be catatonic, atypical and postpartum features.
There are no laboratory tests that diagnose this disorder, but sleep and EEG abnormalities can be tested. There are also hormonal disturbances and brain imaging may shoe increased blood flow in limbic and paralimbic regions, with decreased blood flow in the lateral prefrontal cortex. Late life depression might be associated with altered brain structure and vascular areas.
The presence of this disorder is about 10 to 25 percent for women and 5 to 12 percent for men. On an annual basis, 5 to 9 percent of women and 2 to 3 percent of men will undergo Major Depressive episodes. Children are equally affected, but adolescents and adults show that major depression may be twice as common in women.
The episodes can begin at any age. Two thirds of those who have episodes will have a complete recovery. For those who have only a partial recovery, some individuals may go for many years between episodes and others will have an increasing likelihood of more episodes as they age.
Treatments commonly consist of talk therapy and antidepressants.
Mental Health.com "Major Depressive Disorder"
Depression Today, "DSM-IV Major Depressive Episode"
Psych Central: "Major Depression"