Brainstem in Machado-Joseph disease: Atrophy or small size?

Machado-Joseph disease (MJD), one of the most common types of hereditary spinocerebellar degeneration caused by abnormal expansion of the CAG repeat in the MJD1 gene, presents atrophy of the infratentorial structures neuropathologically and neuroradiologically. Although a significant positive correlation has been reported between infratentorial atrophy and the number of expanded CAG repeat units, the exact changing course of brainstem size in the individual case remains to be resolved. We investigated seven cases of genetically confirmed MJD longitudinally by magnetic resonance imaging with observation periods of 4.5-10.6 years. Measurement of the midsagittal areas of infratentorial structures disclosed progressive atrophy of the pontine base and cerebellum, which correlated significantly with age, whilst midbrain and pontine tegmentum showed atrophy with no significant progression, suggesting it was better identified as 'small size' and might have mostly been completed before the initial symptoms. Such differences between regions in atrophy progression must be caused by a difference in the neuropathological course.