The risk that a patient with recurrent depressive disorder will have an episode of mania never disappears completely, however many depressive episodes he or she has experienced. If a manic episode does occur, the diagnosis should change to bipolar affective disorder.

Recurrent depressive episode may be subdivided, as below, by specifying first the type of the current episode and then (if sufficient information is available) the type that predominates in all the episodes.

Includes:
* recurrent episodes of depressive reaction, psychogenic depression, reactive depression, seasonal affective disorder
* recurrent episodes of endogenous depression, major depression, manic depressive psychosis (depressed type), psychogenic or reactive depressive psychosis, psychotic depression, vital depression

Excludes:
* recurrent brief depressive episodes

In typical depressive episodes of all three varieties described below (mild, moderate, and severe), the individual usually suffers from depressed mood, loss of interest and enjoyment, and reduced energy leading to increased fatiguability and diminished activity. Marked tiredness after only slight effort is common. Other common symptoms are:

(a) reduced concentration and attention;
(b) reduced self-esteem and self-confidence;
(c) ideas of guilt and unworthiness (even in a mild type of episode);
(d) bleak and pessimistic views of the future;
(e) ideas or acts of self-harm or suicide;
(f) disturbed sleep;
(g) diminished appetite.

The lowered mood varies little from day to day, and is often unresponsive to circumstances, yet may show a characteristic diurnal variation as the day goes on. As with manic episodes, the clinical presentation shows marked individual variations, and atypical presentations are particularly common in adolescence. In some cases, anxiety, distress, and motor agitation may be more prominent at times than the depression, and the mood change may also be masked by added features such as irritability, excessive consumption of alcohol, histrionic behaviour, and exacerbation of pre-existing phobic or obsessional symptoms, or by hypochondriacal preoccupations. For depressive episodes of all three grades of severity, a duration of at least 2 weeks is usually required for diagnosis, but shorter periods may be reasonable if symptoms are unusually severe and of rapid onset.

Some of the above symptoms may be marked and develop characteristic features that are widely regarded as having special clinical significance. The most typical examples of these "somatic" symptoms are: loss of interest or pleasure in activities that are normally enjoyable; lack of emotional reactivity to normally pleasurable surroundings and events; waking in the morning 2 hours or more before the usual time; depression worse in the morning; objective evidence of definite psychomotor retardation or agitation (remarked on or reported by other people); marked loss of appetite; weight loss (often defined as 5% or more of body weight in the past month); marked loss of libido. Usually, this somatic syndrome is not regarded as present unless about four of these symptoms are definitely present.

The categories of mild, moderate and severe depressive episodes described in more detail below should be used only for a single (first) depressive episode. Further depressive episodes should be classified under one of the subdivisions of recurrent depressive disorder.

These grades of severity are specified to cover a wide range of clinical states that are encountered in different types of psychiatric practice. Individuals with mild depressive episodes are common in primary care and general medical settings, whereas psychiatric inpatient units deal largely with patients suffering from the severe grades.

Acts of self-harm associated with mood (affective) disorders, most commonly self-poisoning by prescribed medication, should be recorded by means of an additional code from Chapter XX of ICD-10 (X60-X84). These codes do not involve differentiation between attempted suicide and "parasuicide", since both are included in the general category of self-harm.

Differentiation between mild, moderate, and severe depressive episodes rests upon a complicated clinical judgement that involves the number, type, and severity of symptoms present. The extent of ordinary social and work activities is often a useful general guide to the likely degree of severity of the episode, but individual, social, and cultural influences that disrupt a smooth relationship between severity of symptoms and social performance are sufficiently common and powerful to make it unwise to include social performance amongst the essential criteria of severity.

The presence of dementia or mental retardation does not rule out the diagnosis of a treatable depressive episode, but communication difficulties are likely to make it necessary to rely more than usual for the diagnosis upon objectively observed somatic symptoms, such as psychomotor retardation, loss of appetite and weight, and sleep disturbance.

Includes:
* single episodes of depression (without psychotic symptoms), psychogenic depression or reactive depression)

At least two of the three most typical symptoms noted for mild depressive episode should be present, plus at least three (and preferably four) of the other symptoms. Several symptoms are likely to be present to a marked degree, but this is not essential if a particularly wide variety of symptoms is present overall. Minimum duration of the whole episode is about 2 weeks.

An individual with a moderately severe depressive episode will usually have considerable difficulty in continuing with social, work or domestic activities.