Eye signs in patients with parkinsonism: do they predict the development of multiple system atrophy?

This Practice Point commentary discusses Anderson et al .'s study of oculomotor function in multiple system atrophy (MSA). After comparing their findings with those in other disorders, the authors identified four signs ('red flags') that may distinguish the parkinsonian variant of MSA from Parkinson disease, and two signs that may exclude the diagnosis of MSA. This commentary outlines several issues to consider before adopting oculomotor signs as predictors of MSA, including the study's high proportion of patients with late-stage MSA, its use of data from previous studies without matching for patient or study variables, the confounding effect of combining data from parkinsonian and cerebellar variants of MSA, conflicting data reported in previous studies, and the effect of disease prevalence on the positive predictive value of such signs. The diagnostic utility of oculomotor signs in predicting MSA will remain unclear until their positive predictive value is determined in relevant patient groups.