Imaging in multiple system atrophy

The diagnosis of multiple system atrophy and its differentiation from Parkinson's disease can be challenging, particularly in early disease. Both structural and functional imaging studies can be helpful for making the diagnosis, and could potentially be used to monitor disease progression. Magnetic resonance imaging can show distinctive patterns of atrophy and signal changes in multiple system atrophy, such as the “hot cross bun” and hyperintense putaminal rim signs, which are relatively specific, but have low sensitivity. Diffusivity might be particularly helpful in differentiating multiple system atrophy from Parkinson's disease, and appears to change over time, although the correlation with changes in motor dysfunction is uncertain. Diffusion weighted imaging changes in the middle cerebellar peduncle can also reliably separate multiple system atrophy from progressive supranuclear palsy. Volumetry detects characteristic patterns of atrophy. Alterations in spectroscopic patterns and abnormal iron deposition have also been reported. Positron emission tomography or single‐photon emission computed tomography measures of striatal dopamine innervation are abnormal in multiple system atrophy and Parkinson's disease; the addition of dopamine D2 receptor imaging (preserved in Parkinson's disease) can be helpful in differentiating the two. However, fluorodeoxyglucose positron emission tomography shows different characteristic metabolic networks in the two conditions that change with disease progression, and is probably more useful. Functional imaging can also be used to detect changes in cholinergic innervation in multiple system atrophy, and to study neuroinflammation. Imaging of cardiac sympathetic innervation can also differentiate between Parkinson's disease and multiple system atrophy, and might be underutilized for this purpose.