Phosphorylated a-synuclein immunoreactivity in the posterior pituitary lobe

Parkinson's disease is now recognized as a major form of a-synucleinopathy involving both the central and peripheral nervous systems. However, no research has focused on the posterior pituitary lobe (PPL), despite the fact that this organ also plays an important role in systemic homeostasis. In the present study, we aimed to distinguish phosphorylated a-synuclein (paSyn)-positive deposits in the PPL, as is observed in Lewy body- and non-Lewy body-related disorders. PaSyn deposits were immunohistochemically analyzed using formalin-fixed, paraffin-embedded PPL specimens obtained from 60 autopsy cases. Among the cases with Lewy body-related disorders, PPL paSyn deposits were observed in almost all cases of Parkinson's disease (22/23), and in one case of dementia with Lewy bodies (1/1). On the other hand, only 3/36 cases of non-Lewy body-related disorders had paSyn immunoreactivity in the PPL. The present study confirms the presence of paSyn-positive deposits, as demonstrated by high specificity (97.1%) and sensitivity (88.5%), in both Parkinson's disease and dementia with Lewy bodies, suggesting that this finding can be a useful hallmark of Lewy body-related disorders.