Background: The impact of nusinersen therapy on outcomes in adults with Spinal Muscular Atrophy (SMA) remains uncertain.
Objective: To demonstrate whether nusinersen therapy, at currently prescribed doses, can stabilize or improve motor function in adults with SMA using existing outcome measures.
Methods: A single-center prospective cohort study of 6 adults with SMA type 3, with inclusion/exclusion criteria intended to optimize the ability to demonstrate change using established outcome measures. Primary outcomes were the Hammersmith Functional Motor Scale-Expanded (HFMSE) and the Revised Upper Limb Measure (RULM). Secondary outcomes were the PedsQL Fatigue scale, the SMA Functional Rating Scale (SMAFRS), and the 6-minute and 10-meter walk tests (6 MWT and 10 MWT). Estimates of change in HFMSE and RULM mean scores across visits were calculated using a linear mixed effects model. Change from baseline was used for other outcome measures.
Results: HFMSE and RULM scores over 12 months were stable or improved in all participants, with a mean increase of 2 points in each. Other measures showed high intra-individual variability. Adverse events related to the primary diagnosis, including injury and infection, significantly impacted the ability to reliably perform walk tests in the four ambulatory participants.
Conclusions: HFMSE and RULM show potential as responsive outcome measures of motor function in ambulatory and non-ambulatory adults with SMA type 3. A time-dependent accrual of benefit of nusinersen on motor function was apparent in this cohort. More sensitive alternative measures of quality of life, fatigue, exercise tolerance, stability and ADLs are clearly needed for adults with SMA.
Keywords: Spinal muscular atrophy; adult; antisense oligonucleotides; exercise tolerance; treatment outcome.