The coexistence and differentiation of late onset Huntington's disease and Alzheimer's disease. A case report and review of the literature.

The case report presented is clinically compatible with late onset HD. The diagnosis was initially obscured by a lack of family history due to the early death of both parents and siblings. The presence of symptoms at the age of 59 in one offspring is consistent with the intrafamilial transmission of late onset HD disease. The early neuropsychometric data were consistent with the cognitive changes of HD, particularly with the loss of higher cognitive functions, memory and the relative decline in the performance IQ with the preservation of language skills. The psychiatric symptoms of emotional lability and apathy were also congruent with the diagnosis of HD. The atypical features of this patient's course, including progressively severe dementia, seizures and rigidity, may have provided clinical clues to the coexistence of both AD and HD. The absence of caudate atrophy on serial CT scans in this patient, although inconsistent with the gross findings reported on postmortem exam, perhaps could be explained by the 3 1/2-year interval between the last CT scan and death. Further, it has been noted previously that pathological changes tend to lag behind the clinical manifestations of the disease. The pathologic findings on autopsy were confirmatory for the presence of both AD and HD in this patient. Genetic counseling for this family is now most appropriate.