Amyotrophic lateral sclerosis and Alzheimer's disease--clinical and neuropathological considerations in two cases.

Amyotrophic lateral sclerosis (ALS) may be accompanied by cognitive impairment; when present, it is mainly in the form of frontotemporal impairment. We report on two cases with clinically defined ALS that subsequently developed dementia. Neuropathological examination showed not only the typical neuropathological hallmarks characteristic of ALS but, surprisingly, also showed neurofibrillary tangles and neuritic plaques in sufficient numbers to fulfill the diagnostic criteria of definite Alzheimer's disease.