A major depressive episode is characterized by a depressed, disinterested or irritable mood, associated with the loss of interest or pleasure in all or almost all activities, accompanied by a number of other symptoms. These additional symptoms include a reduced capacity for enjoyment, reduced interest in surroundings, difficulty concentrating, lethargy, sleep disturbances, appetite disturbances, decreased self-esteem and self-confidence, and frequent ideas of guilt or worth- lessness. Although older persons are somewhat less likely to report a specific decrease in their mood, they almost always describe a loss of interest in usual activities (anhedonia) in the midst of a major depressive episode. The categories of severe depressive episode in ICD-10 and major depressive episode in DSM-IV are very similar. DSM-IV and ICD-10 permit the diagnosis of a minor depressive episode (in the appendix of DSM-IV and categorized as mild in ICD-10); that is, a depressive episode which fulfils some of the symptom criteria for a major depressive episode and/or dysthymia and which lasts two weeks or longer. The more severe consequences of a depressive episode, such as a successful suicide or a retardation that progresses to stupor, would be characteristic of a severe but not a mild depressive episode in ICD-10.

Older persons who suffer a complicated, severe depression are easily diagnosed according to both ICD-10 and DSM-IV criteria. Problems do arise, however, when the episode experienced by older persons is accompanied by a severe medical illness or significant cognitive impairment. The frequency of psychobiologic symptoms in more severe depressions renders the distinction between symptoms of depression and symptoms of physical illness/functional impairment difficult in the midst of a depressed mood associated with medical illness. The current nosology is not helpful in disaggregating mood disorders from either the symptoms of physical illness or normal psychological reactions to physical illness. Some have suggested that a unique criterion for older persons with depression and cognitive impairment should be instituted (but this is yet to be included in any extant diagnostic system). The co-morbidity of depressive symptoms in cognitive disorders such as dementia, Parkinson’s disease and small strokes renders such an approach potentially useful in improving the current nosology. Two examples are presented below.

‘Vascular depression’ has been proposed as the diagnostic entity secondary to vascular lesions in the brain and appears to increase in frequency with age³. The clinical presentation may differ from major depression, even if only in subtle ways. Elders with vascular depression exhibit impairment in set shifting, verbal fluency, psychomotor speed, recognition memory and planning (executive cognitive function), a ‘depression-executive dysfunction syndrome’ characterized by psychomotor retardation, and reduced interest in activities. Vascular depression is associated with an absence of psychotic features, less likelihood of a family history, more anhedonia and greater functional disability when compared with nonvascular depression.

Others have proposed a depression of Alzheimer’s disease⁴. The criteria are as follows. In persons who meet criteria for dementia of the Alzheimer’s type, three of a series of symptoms that includes depressed mood, anhedonia, social isolation, poor appetite, poor sleep, psychomotor changes, irritability, fatigue or loss of energy, feelings of worthlessness and suicidal thoughts must be present for the diagnosis to be made.