Clinical and Laboratory Features Predict Phenoconversion from Sporadic Adult-onset Ataxia to Multiple System Atrophy.

To determine predicting factors and frequency of phenoconversion from sporadic adult-onset ataxia (SAOA) to multiple system atrophy (MSA). We performed a retrospective review of all patients referred for cerebellar ataxia from 1998 to 2018 at Mayo Clinic, Minnesota. We analyzed clinical features, autonomic testing, and imaging for predictors of later diagnosis of MSA. Among 169 patients with ataxia at presentation, 60 (35.5%) phenoconverted to MSA. Clinical features in MSA phenoconverters included: early autonomic symptoms, stridor, and dream enactment behavior. Imaging features in phenoconverters included pontine atrophy and hot cross bun sign. On autonomic testing, MSA phenoconverters had higher supine blood pressures with larger drops, higher median composite autonomic severity scores, and higher percentage anhidrosis than patients with SAOA. Our findings show that at least a third of patients with SAOA phenoconverted to MSA. Clinical features, autonomic testing, and imaging at presentation may be helpful to identify such patients.