2-year Change in Revised Hammersmith Scale scores in a large cohort of untreated paediatric type 2 and 3 SMA participants

The Revised Hammersmith Scale (RHS) is a 36-item ordinal scale developed using clinical expertise and sound psychometrics to investigate motor function in participants with Spinal Muscular Atrophy (SMA). In this study, we investigate median change in the RHS score up to two years in paediatric SMA 2 and 3 participants and contextualise it to the Hammersmith Functional Motor Scale–Expanded (HFMSE). These change scores were considered by SMA type, motor function and baseline RHS score. We consider a new tran-sitional group, spanning crawlers, standers and walkers-with-assistance, and analyse that alongside non-sitters, sitters and walkers. The transitional group exhibit the most de-finitive change score trend, with an average 1-year decline of 3 points. The RHS has a re-duced floor effect compared to the HFMSE, although we show that the RHS should be used in conjunction with the RULM for participants scoring less than 20 points on the RHS. In the stronger participants (between 10 and 42 on the RHS) in the 5-7 age group, both the RHS and HFMSE can detect 1-year change. The timed items in the RHS have high between-participant variability, so participants with the same RHS total can be differentiated by their timed test items.