Is there pure vascular dementia in old age?

Vascular dementia (VaD) has been suggested to be the most common form of dementia in old age, but clinico-pathologic studies showed big differences in its epidemiology. A retrospective hospital-based study of the frequency and pathology of "pure" VaD (due to cerebrovascular disease without other pathologies) was performed in 1110 consecutive autopsy cases of demented elderly in Vienna, Austria. It assessed clinical, general autopsy data and neuropathology including immunohistochemistry. Neuropathologic diagnosis followed current consensus criteria. Four age groups (7th to 10th decades) were evaluated. "Pure" VaD was observed in 10.8% of the total cohort, decreasing from age 60 to 90+. 85-95% had histories of diabetes, morphologic signs of hypertension, 65% myocardial infarction/cardiac decompensation, and 75% a history of stroke(s). Neuritic AD-pathology was low (mean Braak stages 1.2-1.6). Morphologic subtypes (multi-infarct (MID), subcortical arteriosclerotic (SAE)-the most frequent, and strategic infarct dementia (SID)) showed no age-related differences. By contrast, AD (without vascular or Lewy pathologies), mixed dementia (AD+cerebrovascular encephalopathy), and AD with minor cerebrovascular lesions increased with age. AD+Lewy pathology and other dementias decreased significantly over age 90. This retrograde study using strict morphologic diagnostic criteria confirmed the existence of "pure" VaD in old age, with a tendency to decline at age 90+, while AD and AD+cerebrovascular pathologies showed considerable age-related increase. Another autopsy study distinguishing two age groups of demented showed a significant increase of both AD and cerebral amyloid angiopathy (CAA), but decrease of VaD over age 85, while in a small subgroup of old subjects CAA without considerable AD-pathology may be an independent risk factor for cognitive decline.