Actually LATE, which stands for age-related TDP-43 encephalopathy.
The clinical diagnosis of Alzheimer’s is less than 80% accurate, using MRI, but without the benefit of amyloid or tau PET scans, which are not widely available. Even at post-mortem many patients have mixed pathology, mainly Alzheimer’s, small vessel disease, and Lewy bodies. Another less well understood condition is tau-related cognitive decline, which may explain why some patients who are thought to have Alzheimer’s dementia do not worsen.
The disease termed LATE is recently recognized and is related to a certain protein found in over 20% of people older than 80. Recall that amyloid is found in one-third of the elderly and all do not progress to symptomatic Alzheimer’s probably because of cognitive reserve. Higher levels of education and maintaining cognitive and social activities late in life are thought to underpin this reserve.
The pathological matrix underpinning dementia is more complex than we thought even just several years ago.
See the article by Nelson et al in Brain, April 30, 2019.