α-Synuclein pathology in Parkinson’s and Alzheimer’s disease brain: incidence and topographic distribution—a pilot study

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Abstract
To study the incidence and topographic distribution of α-synuclein-positive inclusions in Parkinson’s disease (PD), dementia with LB (DLB), and Alzheimer’s disease (AD), 206 brains of elderly patients, including 53 patients with clinical PD, 110 autopsy-proven AD cases, 22 with dementia with LB (DLB), 1 case with essential tremor, and 20 age-matched controls were investigated using α-synuclein immunohistochemistry. For technical reasons, the olfactory system was not studied. In all PD brains, α-synuclein-positive inclusions and neuronal losses were present in medullary and pontine nuclei, locus coeruleus, and substantia nigra, with additional lesions in amygdala (24%), allocortex (58%), cingulate area (34%), and isocortex (26.5%). All PD cases corresponded to pathology stage 4–6 suggested by Braak et al. (2003, Neurobiol Aging 24:197). In most cases of DLB, the distribution of α-synuclein pathology and neurodegeneration corresponded to stages 5 and 6 of PD pathology. The case with essential tremor and 48.2% of the AD cases showed no LB pathology; in the other AD brains α-synuclein-positive inclusions were seen in various brain areas. None of the controls showed LB pathology. Among 12 cases of incidental Lewy body disease (without clinical parkinsonian signs), 7 corresponded morphologically to PD stage 3 or 4. In further 6 AD cases, 2 with parkinsonian symptoms, considerable damage to locus coeruleus, substantia nigra, nucleus basalis and allocortex with preservation of the medullary nuclei was seen. The preliminary data largely confirm the Braak staging of brain pathology, although some of the clinical PD cases corresponded to stage 3 often considered as “preclinical”. In addition, some cases without demonstrable involvement of medullary nuclei showed extensive PD-like pathology in other brain areas, suggesting deviation from the proposed stereotypic expansion pattern and that incidental LB pathology may affect solely the locus coeruleus and substantia nigra. Striking similarity of LB pathology between DLB and PD suggests close morphological relationship between both disorders. Widespread LB lesions occurred in many sporadic AD cases without parkinsonian symptoms, the pathogenesis and clinical impact of which are unclear. The relationship between AD and PD with particular reference to synaptophysin-positive lesions needs further elucidation.