[Late onset Huntington's disease - a differential diagnosis of Alzheimer's disease].

A 66-year-old patient was admitted to our memory clinic for diagnostic evaluation of potential Alzheimer's disease (AD). Her family reported progressive disturbances of memory, irritability, fidgetiness, and abrupt movements of the extremities and the head for the last 3 to 4 years. Family history was positive for progressive cognitive deterioration associated with movement disturbances beginning at the age of 65 years. Examination revealed mild dementia as well as involuntary choreatiform movements of the extremities and the head. Genetic testing showed an expanded CAG repeat of 41 in the Huntington's disease (HD) gene leading to the diagnosis of HD with mild dementia. Because the age of onset of HD is typically between 35 to 50 years, HD is rarely considered as a differential diagnosis for dementia in elderly patients. This case shows the relevance of an accurate differential diagnosis of cognitive disturbances in order to detect rare causes of dementia.