Alzheimer’s disease, the most common form of dementia among nursing home residents and other seniors, may not be as prevalent as commonly believed. New research indicates that Alzheimer’s diagnoses often may be wrong.

Only about half of 211 study subjects diagnosed with Alzheimer’s while alive were found during autopsies to have brain conditions commonly association with the disease, researchers said. Alzheimer’s-related brain conditions often absent included amyloid plaques and neurofibrillary tangles. Most of the unconfirmed Alzheimer’s patients had other brain abnormalities, such as hippocampal sclerosis and generalized brain atrophy, researchers noted.

“Larger studies are needed to confirm these findings and provide insight as to how we may more accurately diagnose and prevent Alzheimer’s disease and other principal dementing disease processes in the elderly,” said researcher Lon White, MD, MPH, of the Kuakini Medical System in Honolulu. Study results, which have not yet undergone peer review, will be presented in April at the American Academy of Neurology annual meeting.