The duration of an episode of depression is an important diagnostic criterion. Typically, a depressive disorder lasts at least 2 weeks, and a major depressive episode lasts at least 2 years.
According to some researchers, clinically expressed depressive disorders take on a chronic course in 1/3 of cases, and in the remaining patients , repeated episodes are observed in 70 %. The transition of a major depressive episode to a chronic form is observed in 10 % of men and 20 % of women. Bipolar disorders become chronic in only 1 % of the population.
Depressive disorders have a high risk of recurrence, exacerbation and a tendency to develop chronic forms. Epidemiological studies have shown that 3-5% of the population of their duration exceeds two years, from 12.5% – more than 5 years, and patients with chronic depression observed at the psychiatrist range from 26 to 30% of cases.
According to Russian scientists, depression lasts for about 2 years in every 5th patient . Before starting antidepressant medication, the depressive episode usually lasted for about a year. With modern treatment, a depressive episode lasts on average about 4-6 months. However, as the disease progresses, exacerbations become more frequent, the duration of the interval between 5 – 6 episodes set in 6 – 9 months, to be replaced in the future trend towards less frequent relapses and leads to the fact that the average for the entire life of the patient transfers 7-9 phases.
Depression usually develops slowly over several weeks. Previously, “acute melancholy” was distinguished with the duration of the illness from several weeks to a year or more; “Chronic melancholy” – a disease that lasts for several years (usually the symptoms are more or less mild) and “periodic melancholy”.
Intermittent depressive disorder (recurrent depression) is characterized by cyclical development. The second episode occurs in 75 – 80% of cases within 4-6 months after the first. The transition from a recurrent depressive disorder to a bipolar type of course (periodic change of the depressive phase and manic) is noted in 5-20% of cases. In 50% of cases, this occurs after the first depressive episode, in the rest – after 2-4.
It should be noted that with the introduction of antidepressants into medical practice, the number of erased, masked depressions has increased .