Alzheimer disease with amygdala lewy bodies: A distinct form of α-synucleinopathy

Lewy bodies (LBs) are α-synuclein-immunoreactive neuronal inclusions with a predilection for specific cortical and subcortical regions, including the amygdala. In this study, the presence of LBs was assessed in 347 cases of Alzheimer disease (AD). In 87 cases, LB pathology was diagnostic of brainstem (n = 3), transitional (n = 32), or diffuse (n = 52) Lewy body disease (LBD). The remaining 260 cases of AD were screened for amygdala LBs (AD/ALB) and 62 (24%) cases were found. If AD/LBD cases are included, LBs were detected in 149 (43%) cases of AD. The presence α-synuclein pathology was assessed in multiple brain regions of the 62 cases of AD/ALB and 57 randomly selected cases of AD, and only sparse α-synuclein pathology was detected in both. The burden of α-synuclein pathology in brainstem nuclei, amygdala, and neocortex was significant lower in AD/ALB than in AD/LBD. In comparison to AD/LBD, AD/ALB did not differ in age at death, disease duration, male-to-female ratio, brain weight, Braak neurofibrillary tangle stage, average senile plaque density, or apolipoprotein E ε4 allele frequency. The results suggest that AD/ALB is pathologically different from AD/LBD, suggesting that it is a neuropathologically distinct and isolated α-synucleinopathy.