Identification of a pre-possible multiple system atrophy phase.

A pre-possible MSA phase exists. Improved earlier diagnosis of MSA depends on the sensitivity and positive predictive value of autonomic features or autonomic function tests and on the sensitivity of "atrophy on magnetic resonance imaging of the putamen, middle cerebellar peduncle, pons, or cerebellum" and "new or increased snoring" during the pre-possible MSA phase.