Distinguishing between neurodegenerative disease and disease-free aging: Correlating neuropsychological evaluations and neuropathological studies in centenarians

Objective: In an examination of disease-free aging and neurodegenerative disease in 100-year-olds, the New England Centenarian Study compared data from neuropsychological evaluations with postmortem brain studies of fourteen 100-year-olds to ascertain if the presence or absence of Alzheimer disease changes correlated with measured cognitive abilities. Methods: Fourteen of 74 centenarians who underwent annual extensive neuropsychological evaluation proceeded to postmortem neuropathological examination. CERAD criteria, emphasizing neuritic amyloid plaques and Braak and Braak staging of neurofibrillary tangles were used to assess the 14 brains. Results: Neuropsychological and neuropathological findings correlated well for four subjects with no dementia on testing (CDR = 0) and for six subjects with CDR scores in the dementia range (CDR = 1-5). In the latter group, Alzheimer's disease was diagnosed in four brains; Pick's disease was an etiological factor in the fifth and hippocampal sclerosis in the sixth. Correlation was low for four subjects: two subjects with no dementia on neuropsychological testing met CERAD neuropathological criteria for possible AD; two subjects with dementia on testing did not meet CERAD criteria for definite Alzheimer's disease and had otherwise minimal changes to correlate with the cognitive findings. Conclusions: Lack of correlation between level of cognitive functioning and brain pathology in two subjects with no dementia raised the question of whether a functional reserve delayed the functional expression of pathological changes. For two subjects with dementia on testing, there appeared to be no sufficient pathological explanation for the extent of the cognitive changes: depression and such factors as environment, sensory impairment, and medical illness may all have played a role. There may also have been neuropathologic changes not detected by current methods.