YOMSA is defined as the onset of MSA before age 40 years. There is limited information about the disease course and outcome in these patients.

We retrospectively reviewed medical records of all patients with a diagnosis of clinically established or clinically probable MSA who were evaluated at all Mayo Clinic sites from 1998 to 2021. We identified patients who were ≤40 years at time of disease onset. We evaluated clinical characteristics, disease course, and autonomic function testing results. Composite Autonomic Severity Score (CASS) was calculated based on autonomic testing.

Of 1496 patients with a diagnosis of clinically established or probable MSA, 20 patients had YOMSA. The mean age of onset was 38.61 (±2.16) years; 13 patients (65%) were male. MSA-parkinsonism was the most common subtype (65%). At the time of medical record review, 15 patients were deceased with a mean age of death of 47.88 (±3.83) years. The median duration of disease course (onset to death) and onset to diagnosis were 7.67 [IQR: 6.36, 10.23] and 4.90 [IQR: 3.70, 8.61] years, respectively. Patients with autonomic symptoms at the time of disease onset had a shorter disease course compared to those without autonomic complaints (6.60 years versus 10.74 years; p=0.037). At the time of YOMSA diagnosis, thermoregulatory sweat test was performed in 17 patients with a median of 88% anhidrosis; CASS was available in 19 patients with a median of 5 [IQR: 4, 6.5]. Genetic evaluations were performed in 6 patients with no revealing results. 

Patients with YOMSA are often diagnosed late in the disease course. Those with autonomic symptoms at the time of disease onset have a more rapid course compared to those with initial motor-only presentation.