The co-occurrence of Alzheimer's disease and Huntington's disease: a neuropathological study of 15 elderly Huntington's disease subjects.

BACKGROUND: Dementia is a common feature in both Huntington's disease (HD) and Alzheimer's disease (AD), as well as in the general elderly population. Few studies have examined elderly HD patients with dementia for neuropathologic evidence of both HD and AD. OBJECTIVE: We present neuropathological findings in a retrospective case series of 15 elderly HD patients (ages 60-91 years), 11 of whom had prominent clinical dementia. METHODS: Post-mortem brain tissue was examined and stained for evidence of both HD and AD including Vonsattel grading and Htt-repeat expansion, Bielskowsky, tau, ß amyloid, and TDP43 immunostaining. RESULTS: Mean age at death was 76.8 years, mean disease duration was 18.6 years, and mean CAG repeat expansion was 42. Evidence of AD in addition to HD pathology was present in 9 of 11 (82%) patients with prominent dementia, suggesting that AD may be more commonly co-occurring with HD than previously appreciated. Two patients had only HD as the basis of dementia and four patients did not have prominent dementia. One patient with marked parkinsonian features was not L-dopa responsive and had no substantia nigra Lewy bodies at autopsy. CONCLUSIONS: Our study suggests that AD may frequently contribute to cognitive decline in elderly HD patients which complicates the assessment and management of such individuals. Further study is needed to determine if there is a higher incidence of AD in persons with HD compared to the general population. In addition, our series includes one HD patient whose clinical features masqueraded as Parkinson's disease but was not responsive to levodopa therapy.