Mixed Dementias

Abstract

The term 'mixed dementia' is used to describe adult-onset dementia due to a combination of various etiologies. In contrary to the general principle of medical sciences "one cause-one disease" concept, this term is used to describe patients having both Alzheimer's disease and vascular dementia. The data on mixed dementia indicate the presence of a relation, more than by chance alone, between the two pathological processes. The evidence are microvascular pathology in Alzheimer's disease, causal relationship between stroke and dementia, resemblance of the clinical courses of vascular dementia and Alzheimer's disease at least in some of the patients, identical vascular and genetic risk factors, white matter abnormalities, cholinergic deficits and response to treatment. Pathological, clinical and epidemiological studies suggest relation and/or interaction between vascular dementia and Alzheimer's disease. Vascular pathology contribute to the development of dementia with mechanisms other than infarction. At least in sporadic Alzheimer's disease cases, effects of vascular pathology should be taken into consideration. According to our current clinical approach, the diagnosis of mixed dementia must include the following criteria(¹) the clinical diagnostic criteria of both Alzheimer's disease and vascular dementia;(²) Hachinski ischemic score of 5-6(³) hippocampal atrophy consistent with Alzheimer's disease along with cerebrovascular lesions on neuroimaging studies. Definite mixed dementia diagnosis is possible only in a patient with both stroke and dementia having pathologic findings of Alzheimer disease. This leads to problems of sensitivity and specifity in forming diagnostic criteria. In the future, Bayesian approach with its mathematical basis, probably will be more important in developing diagnostic criteria for mixed dementia.