To examine the appropriateness and clinical relevance of expressing trial results as a percentage slowing of clinical progression between treatment and placebo in Multiple System Atrophy (MSA), and to identify the threshold at which such a difference becomes clinically meaningful.

Treatment effects have been assessed and reported as absolute changes from baseline at a fixed time point. However, there is growing interest in evaluating trial outcomes as percentage changes over the entire treatment duration – particularly in the context of therapies with potential to slow clinical progression of neurodegenerative conditions such as MSA.

Consensus was reached on the appropriateness of expressing treatment effect as percentage-wise slowing in UMSARS for the interpretation of clinical progression in MSA. Consensus was reached that percentage-wise slowing at 21% and above would be clinically meaningful. Over 50% agreed the lower range of 16–20% would be clinically meaningful, however, consensus was not met.

An international panel of MSA experts reached consensus that expressing treatment effects as percentage slowing in UMSARS scores is appropriate, identifying a threshold of 21% or greater as clinically meaningful.