Depression and dementia: the multi-faceted relationship.

The relationship between depression and dementia has been noted since antiquity and still eludes our precise understanding. Rosen (1961) notes that in the ninth century A.D. Rhazes, the Persian physician, mentions melancholy as an inevitable condition in the lives of old and decrepit persons. Later, both Robert Burton (Anatomy of Melancholy) and William Shakespeare, among others, commented on the association between cognitive and affective change. It is now established that cognitive change is part of the symptomatology of primary depressive illness and it is, of course, the cardinal feature of the syndrome of dementia. Depressive illness is found predominantly as a condition of the middle-aged and the elderly; 90% of the dementias are found in the senium, i.e. beyond the age of 65. Hence, an association at the very least between depression and dementia is«to be expected. As both depression and dementia are heterogeneous collections of conditions, the precise relationship will, not surprisingly, be a complex one. Furthermore, depressive illness is still classified among the 'functional' psychiatric disorders, i.e. among those conditions which do not have a tangible organic causation, a state of affairs accepted despite its unsatisfactory nature. Evidence is accumulating that a substantial and growing proportion of depressive illnesses have neurobiological correlates and, as techniques advance, the position of some forms, at least, of depressive illness among the' functional' disorders may become an untenable one. The converse applies to dementia. Very early the dementias became equated with 'organic' illness. But as knowledge has grown and our conceptualization of dementia has changed, we are now prepared to accept that the dementia syndrome may have 'organic' as well as 'functional' causation. A recent paper on dementia caused by depression (Rabins et al. 1984) emphasizes this point. Dementia is nowadays defined as an acquired, global condition, with intellectual deterioration, memory impairment and personality disorganization in the presence of unimpaired consciousness (e.g. Lishman, 1978). As depressive illness is acquired, global in its manifestation and occurs in the presence of unimpaired consciousness, it is not difficult to see that any cognitive change in depressive illness, if it progresses to substantial deficits in intellectual, memory or personality functioning, will satisfy the criteria for the syndrome of dementia.