[Epidemiology and comorbidity of depressive disorders]

Recent epidemiological surveys in general populations of different countries of the world found lifetime prevalence rates of major depressions between 3.3% and 17%. For dysthymia (depressed mood over a period of at least two years with at least two concomitant depressive symptoms) the prevalence rate was found to be between 2% and 7%. The prevalence rates of major depressions and dysthymia are usually higher for females than for males. Bipolar disorders can be observed in about 1% of a general population over lifetime, and they seem to be somewhat more common among males than females. Divorced and separated persons have a higher risk of suffering from major depressions than married persons. Major depressions are thought to be more common among members of the lowest social class than among people belonging to the upper classes. Major depressions usually start between the age of 25 and 30 years, and the age of onset of bipolar disorders is between the age of 18 and 30 years. For western industrial nations a secular trend towards an increase in the prevalence of major depressions may be presumed. However, such a secular trend has not yet been confirmed, owing to biases associated with methodological problems. A notable comorbidity of major depressions can be observed with all anxiety disorders, obsessive-compulsive disorders, eating disorders, post-traumatic stress disorder, disorders of impulse control, abuse and dependence of alcohol and of other legal and illegal drugs, pathological gambling, migraine, fibromyalgia and irritable bowel syndrome. This observation has led to the concept of an "affective spectrum". This phenomenon has to be kept in mind during the diagnostic process and treatment.