Background and objectivesAge is the largest risk factor for dementia. However, dementia is not universal, even among the oldest-old age groups. Following contemporary neuropathologic guidelines, our objectives were to describe the key neuropathologic lesions and their associations with antemortem cognition in oldest-old individuals.
MethodsParticipants were those enrolled in The 90+ Study, a longitudinal, population-based study of aging/dementia in the oldest-old, who agreed to postmortem brain examination. All autopsied brains as of December 2020 were evaluated for prevalence of Alzheimer's disease neuropathologic change (ADNC) and non-ADNC neuropathologic comorbidities. Associations between neuropathologic lesions or total neuropathologic burden score (sum of the individual scores) and cognition were assessed using multinomial logistic regression and multiple linear regression. Separate regression analyses evaluated relationships between limbic-predominant age-related TDP-43 encephalopathy (LATE-NC) and hippocampal sclerosis (HS) or ADNC/primary age-related tauopathy (PART). Resistance, or failure to develop ADNC/PART, and resilience, inferred from higher than expected cognitive functioning, were evaluated in the presence or absence of non-ADNC neuropathologic features.
ResultsThe most common neuropathologic features in the sample (n=367) were ADNC/PART-related. Increased dementia odds were associated with elevated total neuropathologic burden (OR=1.5 [95% CI 1.3-1.7] p<0.0001), beta amyloid (OR=1.6 [95% CI 1.2-2.0] p<0.0001), neurofibrillary tangles (OR=2.6 [95% CI 1.7-4.1] p<0.0001), and LATE-NC (OR=2.3 [95% CI 1.7-3.1] p<0.0001), correcting for multiple comparisons. LATE-NC was associated with dementia with (OR=6.1 [95% CI 2.0-18.7] p=0.002) and without (OR=5.0 [95% CI 2.6-9.7] p<0.0001) co-occurring HS, and increased the odds of dementia among participants with ADNC (OR=5.0 [95% CI 2.7-9.2] p<0.0001). Resistance to moderate/severe ADNC/PART was rare (3%), but resilience to ADNC/PART was not (55%). Resilience was rarer in the presence of non-ADNC comorbid lesions, particularly LATE-NC. Among those with moderate/severe ADNC/PART, dementia odds increased with each non-ADNC comorbid lesion (e.g., 1 lesion: OR=2.4 [95% CI 1.3-4.5] p<0.005; 2 lesions: OR=5.9 [95% CI 2.8-12.3] p<0.0001).
ConclusionThese results highlight the importance of non-ADNC neuropathologic comorbidity, predominantly LATE-NC, to cognition in the oldest-old. Given the cumulative effects of non-ADNC comorbid neuropathologic abnormalities, reducing their prevalence, especially LATE-NC, will be vital to the ultimate goal of reducing dementia burden in the oldest-old individuals.