Coexisting depression and dementia in a community survey of the elderly

We report here on the coexistence of dementia and depression in a community population aged 75 years and older. Complete information about mood and cognition was available for 286 cognitively intact subjects selected for assessment because of their low scores on the Mini-Mental State, and for 158 mildly and moderately demented subjects. Severely demented subjects, who were incapable of providing information, were excluded. Five percent (8/158) of demented subjects also fulfilled criteria for major depressive disorder Diagnostic and Statistical Manual of Mental Disorders, third edition (DSM-III) compared with 9% (27/286) of cognitively intact subjects. No substantial differences existed in the symptoms reported by demented depressives and nondemented depressives, but subjects who suffered from both disorders were so markedly apathetic that their depression might easily have been overlooked had specific enquiries not been made. Depression was particularly associated with dementia secondary to multi-infarct and Parkinson's disease. When reviewed one year later, 2 of the 18 surviving depressed, nondemented subjects showed evidence of dementia. Both presented unusual diagnostic difficulties, however, and no evidence emerged that large numbers of elderly people will be misclassified in community surveys that include a mental state examination, cognitive testing, and an informant interview.