Cotton wool plaques in non-familial late-onset Alzheimer disease

Cotton wool plaques (CWP) are large, ball-like plaques lacking dense amyloi d cores that displace adjacent structures. They were first described in a F innish kindred with early-onset Alzheimer disease (AD) with spastic parapar esis due to a presenilin-1 Delta9 mutation. We describe a case of sporadic late-onset AD with numerous neocortical CWP as well as severe amyloid angio pathy and marked leukoencephalopathy, compared with 16 cases of late-onset AD with similar degrees of amyloid angiopathy and leukoencephalopathy. The cases were studied with histologic methods and with single and double immun ostaining for beta-amyloid (A beta), paired helical filaments-tau (PHF-tau) , neurofilament (NF), glial fibrillary acidic protein (GFAP), HLA-DR, and a myloid precursor protein (APP). We found that CWP were well-circumscribed a myloid deposits infiltrated by ramified microglia and surrounded by dystrop hic neurites that were immunopositive for APP, but only weakly for NF and P HF-tau. A beta1-12 was diffuse throughout the CWP, while A beta 37-42 was p eripherally located and A beta 20-40 more centrally located. Two of the 16 late-onset AD cases also had CWP, but they were also admixed with diffuse p laques and plaques with dense amyloid cores. Pyramidal tract degeneration w as not a consistent finding or a prominent feature in any case. The results suggest that CWP are not specific for early-onset familial AD with spastic paraparesis.