There is no general agreement about the best method of classifying depressive disorders. A number of approaches have been tried, based on the following:
● presumed aetiology
● symptomatic picture
● course.
Classification by presumed aetiology
Historically, depressive disorders were sometimes classified into two kinds—those in which the symptoms were caused by factors within the individual, and were independent of outside factors (endogenous depression), and those in which the symptoms were a response to external stressors (reactive depression). However, it has been recognized for many years that this distinction is unsatisfactory. For example, Lewis (1934) wrote:
every illness is a product of two factors—of the environment working on the organism—whether the constitutional factor is the determining influence or the environmental one ... is never a question to be dealt with as either/or.
As noted in Chapter 5, when considering the aetiology of individual cases of depression, the relative contributions of a variety of aetiological factors must be considered. Neither ICD-10 nor DSM-5 contains categories of reactive or endogenous depression.
Classification by symptomatic picture
Melancholic depression
It is well recognized that episodes of depression vary in symptomatic profile both within and between subjects. In the section on clinical description it was noted that some depressive conditions are characterized by
‘biological’ symptoms, such as loss of appetite, psychomotor changes, weight loss, constipation, reduced libido, amenorrhoea, and early-morning waking. These symptoms have sometimes been termed melancholic, and they have been used to delineate a specific subgroup of depressive disorders, namely major depression with melancholia in DSM-5, or depressive episode with somatic symptoms in ICD-10 (see Box 9.2). The difficulty with this classification is that most patients have melancholic symptoms of some kind, although a careful search may be required to reveal them. Therefore the number of symptoms that are needed to fulfil the criterion
Clinical features of depression with ‘somatic’ or ‘melancholic’ features
● Loss of interest or pleasure in usual activities
● Lack of emotional reactivity to normally pleasurable surroundings and events
● Early-morning waking (2 hours or more before
usual time)
● Depression worse in the morning
● Psychomotor agitation or retardation
● Marked loss of appetite
● Weight loss (5% or more of body weight in
last month)
● Marked loss of libido (ICD-10 only)
● Distinct quality of depressed mood (DSM-5 only)
● Excessive guilt (DSM-5 only)
At least four of these symptoms are required to make a diagnosis of depression ‘with somatic features’ (ICD-10) or major depression ‘with melancholic features’ (DSM-5). DSM-5 also specifically requires either ‘loss of interest etc’ or ‘lack of emotional reactivity etc’, to be present.
for depression with melancholia is somewhat arbitrary. Despite this caveat, it is generally agreed that clear-cut melancholic depression is associated with the following clinical correlates (see Parker et al., 2015):
● more severe symptomatology
● family history of depression
● poor response to placebo medication
● possibly better response to tricyclic antidepressants
than selective serotonin reuptake inhibitors (SSRIs)
● more evidence of neurobiological abnormalities (e.g.
decreased latency to rapid eye movement sleep, cortisol hypersecretion).
It is still not clear whether melancholic depression is a distinct subtype or whether it represents a point on a continuum of severity of depression, towards the more severe end. Kendler (1997) attempted to answer this question using a population sample of twins. He found evidence that melancholic depression did represent a valid subtype in that it identified a group of individuals with a particularly high familial risk of depression. However, the diagnosis of melancholia indicated the presence of a quantitatively more severe form of depression, rather than a distinct aetiological subtype.
Psychotic depression
As noted above, severe depression can also be manifested with psychotic features (although in depressive psychosis the features of melancholia are almost invariably present as well). The presence of psychotic features indicates that treatment with antidepressant medication alone is unlikely to be successful, and that combination with antipsychotic drugs is usually needed (Cowen and Anderson, 2015).
Non-melancholic depression
In this classification by symptom profile, the remaining forms of major depression (‘non-melancholic’ depression) include several different kinds of clinical disorder—for example, mild depressive episodes and atypical depression. These depressions are more likely to have a relative prominence of features, such as anxiety, hostility, phobias, and obsessional symptoms. In the past, because of these symptoms, non-melancholic depressions were sometimes called ‘neurotic depression’, but this term does not appear in current diagnostic classifications. As noted above, atypical depression has particular clinical characteristics and in DSM-5 atypical depression, like melancholic depression, can be a specifier for a major depressive episode.
Classification by course
Unipolar and bipolar disorders
Mood disorders are characteristically recurrent, and Kraepelin was guided by the course of illness when he brought mania and depression together as a single entity. He found that the course was essentially the same whether the original disorder was manic or depressive, and so he put the two together in a single category of manic–depressive psychosis.
This view was widely accepted until 1962, when Leonhard and colleagues suggested a division into three groups:
● Patients who had had a depressive disorder only (unipolar depression).
● Those who had had mania only (unipolar mania).
● Those who had had both depressive disorder and
mania (bipolar).
Nowadays, it is the usual practice not to use the term ‘unipolar mania’, but to include all cases of mania in the bipolar group on the grounds that nearly all patients who have mania eventually experience a depressive disorder (see Chapter 10).
Seasonal affective disorder
Some patients repeatedly develop a depressive disorder at the same time of year, usually the autumn or winter. In some cases the timing reflects extra demands placed on the person at a particular season of the year, either in work or in other aspects of their life. In other cases there is no such cause, and it has been suggested that seasonal affective disorder is related in some way to the changes in the seasons (e.g. to the number of hours of daylight). Although these seasonal affective disorders are characterized mainly by the time at which they occur, some symptoms are said to occur more often than in other mood disorders. These symptoms include:
● hypersomnia
● increased appetite, with craving for carbohydrate
● an afternoon slump in energy levels.
The most common pattern is onset in autumn or winter, and recovery in spring or summer. This condition is also called ‘winter depression’. Some patients show evidence of hypomania or mania in the summer, which suggests that they have a seasonal bipolar illness. This pattern has led to the suggestion that shortening of daylight hours is important in the pathophysiology of winter depression, and treatment methods include exposure to bright artificial light during hours of darkness. DSM-5 has a specifier of ‘seasonal pattern’, which can be applied to recurrent major depression with an established seasonal onset. The use of bright light treatment is reviewed in Chapter 25.
Recurrent brief depression
Some individuals experience recurrent depressive episodes of short duration, typically 2–7 days, that are not of sufficient duration to meet the criteria for major depression or depressive episode. These episodes recur with some frequency, about once a month on average. There is no apparent link with the menstrual cycle in female sufferers. Although the depressive episodes are short, they are as severe as the more enduring depressive disorders, and can be associated with suicidal behaviour. Thus recurrent brief depression is associated with much personal distress and social and occupational impairment. Individuals with recurrent brief depression often receive treatment with antidepressant medication, but its value is questionable (see Baldwin and Sinclair, 2015).
Classification in DSM and ICD
The main categories in the sections on depressive disorders in DSM-5 and ICD-10 are shown in Table 9.1 and Box 9.3. Broad similarities are evident, together with some differences. The first similarity is that both systems contain categories for single episodes of mood disorder as well as categories for recurrent episodes. The second is that both recognize milder but persistent depressive states (dysthymia) although, as noted above, in DSM-5 dysthymia has been subsumed into the category of ‘Persistent Depressive Disorder’, which also includes ‘Chronic Major Depression’. In DSM-5, mood disorders that are judged to be secondary to a medical condition are included as a subcategory of mood disorders, whereas in ICD-10 these conditions are classified as mood disorders under ‘Organic Mental Disorders’.
Both ICD-10 and DSM-5 classify depressive episodes on the basis of severity and whether or not psychotic features are present. It is also possible to specify whether the depressive episode has melancholic (DSM- 5) or somatic (ICD-10) features. In DSM-5, an episode of major depression with appropriate clinical symptomatology (see above) can be specified as atypical depression. In ICD-10, atypical depression is classified separately under ‘Other depressive episodes.’ Both ICD- 10 and DSM-5 allow the diagnosis of recurrent brief depression, but under slightly different headings (see Table 9.2). DSM-5 has some additional clinical specifiers which may have implications for treatment and prognosis (Table 9.3).
Classification and description in everyday practice
Although neither DSM-5 nor ICD-10 is entirely satisfactory, it seems unlikely that further rearrangement of descriptive categories would be an improvement. A solution will only be achieved when we have a better understanding of aetiology. Meanwhile, either ICD-10