TSPO and multiple system atrophy: The high variability of microglial activation is also reflected in PET studies of idiopathic Parkinson's disease, with some authors finding a correlation with clinical phenotype, but others failing to do so.22 Because of the lack of TSPO studies in MSA, we can only assume at this stage that the clinical phenotype and severity will not be a simple linear function of the amount and localization of microglial activation.