Objective This study aimed to determine the spectrum of pathological involvement of the striatonigral (StrN) and olivopontocerebellar (OPC) systems in Japanese patients with multiple system atrophy (MSA). This study also aimed to compare the pathological spectrum of Japanese MSA patients with the previously reported results in British MSA patients.

Methods A semiquantitative pathological analysis of 50 MSA patients' brains that were referred to the Brain Research Institute, Niigata University, Japan, was performed. The severity of neuronal cell loss was determined as previously described by the study from the Queen Square Brain Bank (QSBB), UK.

Results The mean neuronal cell loss score was significantly higher in the OPC area than in the basal ganglia sites examined, except the dorsolateral putamen. The relative prevalence of pathological phenotypes showed that 40% of cases had OPC-predominant pathology, 18% had StrN-predominant pathology and the remaining (42%) had equivalent StrN and OPC pathology. None of the MSA cases had coexistent Lewy bodies in the dorsal motor nucleus of the vagus and the substantia nigra.

Conclusions In contrast to the previously reported results involving British patients' brains from the QSBB (OPC-predominant pathology 17%, StrN-predominant pathology 34%, equivalent StrN and OPC pathology 49%), the results of the present study showed more pathological involvement of the OPC system than of the StrN system. The rarity of Lewy bodies may underlie the phenotypic expression of Japanese MSA. The present observations reflect the disequilibrium in the phenotype distribution between the two populations.