An extract from Harvard.
http://www.health.harvard.edu/newsweek/Dysthymia.htm
Dysthymia
Psychotherapists and patients confront the high cost of “low-grade” depression.
(This article was first printed in the February 2005 issue of the Harvard Mental Health Letter. For more information or to order, please go to http://www.health.harvard.edu/mental.)
Depression is a word with many meanings — anything from a passing mood of sadness or discouragement to a condition of inconsolable misery, suicidal thoughts, and even delusions as well as severe physical symptoms. It’s regarded as a clinical disorder when depressed mood and related symptoms are serious enough or last long enough to interfere with work, social life, family life, or physical health.
The Greek word dysthymia means “bad state of mind” or “ill humor.” As one of the two chief forms of clinical depression, it usually has fewer or less serious symptoms than major depression but lasts longer. The American Psychiatric Association defines dysthymia as depressed mood most of the time for at least two years, along with at least two of the following symptoms: poor appetite or overeating; insomnia or excessive sleep; low energy or fatigue; low self-esteem; poor concentration or indecisiveness; and hopelessness.
Dysthymia and major depression naturally have many symptoms in common, including depressed mood, disturbed sleep, low energy, and poor concentration. There are also parallel symptoms: poor appetite, low self-esteem, and hopelessness in dysthymia, corresponding to the more severe symptoms of weight change, excessive guilt, and thoughts of death or suicide in major depression. Major depression may also include two symptoms not found in the standard definition of dysthymia: anhedonia (inability to feel pleasure) and psychomotor symptoms (chiefly lethargy or agitation). An episode of major depression requires at least five symptoms instead of three, but it need last only two weeks rather than two years.
Dysthymia is a serious disorder. It is not “minor” depression, and it is not a condition intermediate between severe clinical depression and depression in the casual colloquial sense. In some cases it is more disabling than major depression. Still, dysthymia is so similar to major depression that the American Psychiatric Association’s diagnostic manual also suggests, as a possibility for further investigation, an alternative definition with symptoms including anhedonia, social withdrawal, guilt, and irritability but not appetite or sleep disturbance. The purpose is to distinguish dysthymia more clearly from major depression by emphasizing mood and personal relations over physical symptoms.
Dysthymia is about as common as major depression. Given its chronic nature, that makes it one of the disorders most often seen by psychotherapists. About 6% of the population of the United States has had an episode of dysthymia at some time, 3% in the last year. As many as a third of patients in psychotherapy may be suffering from dysthymia. Like major depression, it is more common in women than in men, but it tends to arise earlier in life. The American Psychiatric Association distinguishes between this early-onset form and a form that occurs later in life and often comes on less gradually.
More than half of people with dysthymia eventually have an episode of major depression, and about half of patients treated for major depression are suffering from this double depression. Many patients who recover partially from major depression also have milder symptoms that persist for years. This type of chronic depression is difficult to distinguish from dysthymia.