Hippocampal and mesial temporal sclerosis in early-onset frontotemporal lobar degeneration versus Alzheimer's disease.

Hippocampal sclerosis (HS) and mesial temporal sclerosis (MTS) may occur with frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD) as well as with normal aging. Prior studies suggest that HS/MTS may be more closely associated with FTLD but have not directly compared the prevalence and clinical characteristics of HS/MTS between neuropathologically confirmed early-onset (age ≤ 65) cohorts of FTLD and AD. We identified patients with early-onset FTLD (n = 136) and AD (n = 267) from National Alzheimer's Center Consortium databases and compared neuropathological and clinical data between these 2 groups. The FTLD group had a significantly higher prevalence of HS/MTS than that of the AD group. However, HS/MTS was associated with increasing age and memory impairment in the AD group but not in the FTLD group. These findings are consistent with the hypothesis that HS/MTS in FTLD occurs as part of the primary pathological process, rather than as a secondary, nonspecific effect of aging on memory and hippocampal function.