Conversion from subtypes of mild cognitive impairment to Alzheimer dementia

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Abstract
Objective: To compare the rates of conversion to Alzheimer dementia (AD) between subtypes of mild cognitive impairment (MCI) in a community-based birth cohort investigated at age 75 and followed up after 30 months. Methods: The Vienna Trans-Danube Aging Study investigated every inhabitant of the area on the left shore of the river Danube who was born between May 1925 and June 1926. With use of the official voting registry, 1505 subjects were contacted and 697 participated. Data refer to the cohort of 581 nondemented individuals who completed extensive neuropsychological examination at baseline. Follow-up after 30 months was possible in 476 probands (35 deceased). Results: The 141 patients with MCI at baseline were classified into two subtypes. At follow-up, 41 of these patients with MCI were diagnosed with AD. Conversion rates to AD were 48.7% (CI: 32.4 to 65.2) for amnestic MCI and 26.8% (CI: 17.6 to 37.8) for nonamnestic MCI. Another 49 AD cases originated from cognitive health at baseline (12.6%; CI: 9.4 to 16.3). Conclusions: Patients with mild cognitive impairment (MCI) showed a high probability to be diagnosed with Alzheimer dementia (AD) after 30 months. Subtypes of MCI were not useful in defining early stages of various types of dementia: Not only amnestic MCI but also nonamnestic MCI converted frequently to AD, and conversion to vascular dementia and dementia with Lewy bodies was not restricted to nonamnestic MCI.