Morphological features of Pick's and atypical Alzheimer's disease in Down's syndrome.

This is a pathological analysis of a 50-year-old severely mentally retarded female with trisomy 21 who five years prior to her demise developed progressive dementia, epileptic seizures and choreiform movements. The necropsy revealed gross and microscopic features of Alzheimer's and Pick's disease. Ultrastructurally the majority of neurofibrillary changes and all studied Pick bodies consisted of 15 nm straight tubules. A few neurofibrillary changes were composed of 22 nm paired helical filaments, which were also found in the enlarged neurites of neuritic plaques. A few paired helical filaments were interspersed between straight tubules of Pick bodies. These findings in a patient with Down's syndrome and previous reports of atypical features of Alzheimer's disease indicate that very probably our case is a variant of Alzheimer's disease, thus broadening the spectrum of pathological changes observed in Alzheimer's disease.