Heterogeneity and comorbidity in dementiadepression syndromes
Studies of the psychopathology of dementing disorders have demonstrated that depressive manifestations occur in approximately half of the demented patients . In a recent series reported by , about half of the Alzheimer's patients had depressed mood. Approximately 20% of demented psychiatric outpatients have major depression, while 17 to 30 of Alzheimer's patients also meet criteria for major depression (Rovner et al., 1990; Reifler et al., 1986; Wragg and Jeste, 1989). Further, multi-infarct dementia and Parkinsonism (Sano et al., 1989) are strongly associated with depression.
The high comorbidity between depression and dementia raises the question whether depression is a prodromal state of dementia or whether depressives are most vulnerable to development of dementing disorders. Rovner and coworkers (1990) observed that 30% of depressed Alzheimer's patients had history of previous psychiatric illness, and Agbayewa (1986) noted that 18% of Alzheimer's patients had history of psychiatric disorders, mainly depression or paranoia. On the other hand, Murphy (1983) observed that cognitively intact elderly depressives have only a slightly higher probability of developing dementia than the general population. Thus, one must conclude that if depression is associated with vulnerability to dementing disorders, this is true in only a small number of demented patients.
A second question is whether dementing disorders predispose to depression. The percentage of dementing patients in samples of major depressives is approximately 10 times higher than that of the general elderly population (Rovner et al., 1990; Reifler et aZ.,1986; Wragg and Jeste, 1989). However, studies of medical patients show percentages of depression comparable to those of demented patients. These findings challenge the specificity of dementing disorders as a cause of depression in the elderly. On the other