Outcome measures in a cohort of ambulatory adults with spinal muscular atrophy

Muscle Nerve. 2020 Feb;61(2):187-191. doi: 10.1002/mus.26756. Epub 2019 Dec 11.


Introduction: With the advent of disease-altering therapies for spinal muscular atrophy (SMA), there is a requirement to better characterize outcome measures, particularly in milder forms of disease.

Methods: Maximal voluntary isometric contraction testing and 6-minute walk test (6MWT) performed in ambulatory SMA adults as part of the SMA-VALIANT trial were analyzed. Test-retest reliability and correlation with other candidate biomarkers and outcomes were investigated.

Results: Maximal voluntary isometric contraction testing and 6MWT showed good test-retest reliability (intraclass correlation coefficient = 0.98 and 0.85, respectively). Maximal voluntary isometric contraction testing and 6MWT demonstrated very strong correlation (r = 0.83, P <. 0001), and each correlated with the SMA Functional Rating Scale (r = 0.7, P < .0001 and r = 0.65, P = .0001, respectively), lean muscle mass (r = 0.68, P < .0001 and r = 0.56, P = .001, respectively), and ulnar compound muscle action potential (r = 0.57, P = .0008 and r = 0.47, P = .008, respectively).

Discussion: Maximal voluntary isometric contraction testing and 6MWT are suitable outcomes for use in ambulatory adults with SMA. Maximal voluntary isometric contraction testing may be preferable because of superior test-retest reliability and closer associations with other outcomes and biomarkers of neuromuscular function.

Keywords: MVICT; SMA Functional Rating Scale; adults; ambulatory; maximum voluntary isometric contraction testing; six-minute walk test; spinal muscular atrophy.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials
  • Adult
  • Biomarkers
  • Cohort Studies
  • Cross-Over Studies
  • Disease Progression
  • Double-Blind Method
  • Female
  • Humans
  • Isometric Contraction
  • Male
  • Middle Aged
  • Muscle Strength
  • Muscle, Skeletal / pathology
  • Muscular Atrophy, Spinal / diagnosis*
  • Outcome Assessment, Health Care
  • Reproducibility of Results
  • Ulnar Nerve
  • Walk Test
  • Young Adult


  • Biomarkers