Pathologic features of Alzheimer’s disease and dementia are more extreme in younger old persons (age 75) than in older old persons (age 95), according to a study in the May 28 New England Journal of Medicine.
George M. Savva, PhD, and colleagues, from the Institute of Public Health, University of Cambridge in the UK, assessed 456 brains using measures of pathologic features of Alzheimer’s disease, cerebral atrophy, and cerebrovascular disease. The brains had been donated to the Medical Research Council Cognitive Function and Ageing Study; persons (59% women) had been between ages 69 and 103 at time of death. The effect of age on the relationship between neuropathologic lesions and dementia was modeled using logistic regression. Prior to death, dementia was diagnosed in 243 participants.
“Among persons without dementia, the prevalence of moderate or severe neuritic plaques and of neurofibrillary tangles in each area increased with increasing age at death,” Dr. Savva and colleagues stated. These pathologic changes remained constant or tended to decline with age in subjects who died with dementia. “Consequently, the difference in the burden of pathologic lesions between persons who died with and those who died without dementia was less in those who died at older ages,” the authors noted. However, cortical atrophy was more prevalent among those who died with dementia, regardless of age.
A separate analysis compared those who died at age 75 with those who died at age 95. Subjects with dementia showed atrophy of the hippocampus and neocortex at all ages. Those who were age 75 at time of death had a stronger association among neuritic plaques, neurofibrillary tangles, and dementia (OR, 8.63), than those who died at age 95 (OR, 2.48).
“The exponential relationship between age and the prevalence of dementia, combined with the increasing number of people surviving into old age, is driving the prevalence of dementia upward in the oldest old age groups,” Dr. Savva and researchers stated.
The results suggest that therapeutic interventions based only on studies of younger cohorts will be less effective on older old persons. “Age cannot be neglected if the effect of dementia on the population is to be addressed and the most effective strategies are to be developed,” Dr. Savva and colleagues concluded.