Prevalence and pathology of vascular dementia in the oldest-old.

The prevalence of both Alzheimer's disease (AD) and vascular dementia (VaD) increase with advancing age, but epidemiologic data above age 85 are imprecise and inconsistent. A retrospective hospital-based study of the prevalence and pathology of VaD was performed in 1700 consecutive autopsy cases of demented elderly in Vienna, Austria (mean age 84.3 ± 5.4 SD; 90% over age 70). It assessed clinical and general autopsy data and neuropathology including immunohistochemistry. Neuropathologic diagnosis followed current consensus criteria. Four age groups (7th to 10th decade) were evaluated. "Pure" VaD (due to cerebrovascular disease without other pathologies; neuritic Braak stages 1.2-1.6) was observed in 12.3% of the total cohort, decreasing between age 60 and 90+ from 15.0 to 8.7%. Morphologic subtypes (subcortical arteriosclerotic encephalopathy, multi-infarct encephalopathy, and strategic infarct dementia) showed no age-related differences. By contrast, AD (without concomitant pathologies; 45.6% of total), mixed dementia (AD + cerebrovascular encephalopathy; 5.5%), and AD with minor cerebrovascular lesions (22.3%) increased with age. The relative prevalence of AD + Lewy pathology (9.3%) remained fairly stable, whereas other dementias (5.0%) decreased significantly over age 90. 85% of the patients with "pure" VaD had histories of diabetes, 75% of stroke(s), 95% morphologic signs of hypertension, 65% myocardial infarction (recent and old ones), 97% cerebral hypertonic-arteriosclerotic microangiopathy (associated with cerebral amyloid angiopathy in 23%) and 90% severe atherosclerosis of large cerebral arteries. Similar autopsy findings were seen in mixed dementia (MIX) and in AD + minor cerebrovascular lesions. Major vascular lesions differed between VaD and MIX, VaD showing more than 60% subcortical infarcts, MIX only 43% such lesions. This retrograde hospital-based study using strict morphologic diagnostic criteria confirmed the existence of "pure" VaD in old age, with a tendency to decline after age 90, while AD and AD + cerebrovascular pathologies showed considerable age-related increase, and "pure" AD slightly decreasing after age 90.