Alzheimer-type lesions in Huntington's disease.

Cognitive changes in Huntington's disease (HD) are variously related to diffuse cortical atrophy with neuron loss and dystrophic neurites leading to disruption of striato-frontal or limbic circuitries, while recent studies suggest an increasing prevalence of Alzheimer-like lesions in HD brain. A comparative morphological study of 27 autopsy cases of HD (age 34 to 75 years) and of 26 age- and sex-matched non-demented controls was performed. Absence of Alzheimer-type lesions was seen in 33% of HD brains (mean age 49 years); 48% showed early non-neuritic tau pathology in limbic areas (Braak stages I and II) without amyloid deposits occurring as early as age 34 years (mean age 54 years), while Braak stages II and III with amyloid plaques were present in 19%, the youngest such HD patient being 42 years (mean age 54 years). In controls, similar tau pathology changes with later onset (age 45 years) and occurrence of amyloid plaques in 26%--all aged over 60 years--were observed. No probable or definite cases of Alzheimer disease (AD) according to CERAD criteria were seen in both cohorts. Those data confirm previous studies on the rare coexistence of HD and AD, although initial stages of Alzheimer-like lesions develop rather early in HD patients, but obviously show less rapid progress even in advanced age. The reasons for the early onset but mild progress of Alzheimer-like lesions in HD and their contribution to cognitive decline await further elucidation.