The Spinal Muscular Atrophy Health Index: A novel outcome for measuring how a patient feels and functions

Introduction: The Spinal Muscular Atrophy Health Index (SMA-HI) is a multifaceted, disease-specific, patient-reported outcome to measure an SMA patient's perception of their disease burden. In preparation for upcoming therapeutic trials, we examine the validity, reliability, and usability of the SMA-HI in adults, teenagers, and children with SMA.

Methods: Using data from a cross-sectional study of 359 international adult patients with SMA, we identified the most relevant symptoms to include in the SMA-HI. We utilized factor analysis, patient interviews with adults and minors (age 8-15 years), known-group validity testing, and test-retest reliability assessments to evaluate and refine the SMA-HI.

Results: The SMA-HI measures overall disease burden and 15 areas of SMA health. Fifteen adult patients and five patients, age 8 to 15 years, participated in semistructured qualitative interviews and found the SMA-HI to be comprehensive, easily completed, and to have clear meaning. The final SMA-HI and its subscales demonstrated good internal consistency (Cronbach α = 0.77-0.96), high test-retest reliability (intraclass correlation coefficient = 0.60-0.96), and an ability to differentiate between SMA groups with different disease severities affecting areas such as employment and ambulation (P < .0001 for both).

Discussion: This research provides evidence that the SMA-HI is a valid, relevant, and reliable outcome measure to assess multifaceted patient-reported disease burden in older children, teenagers, and adults with SMA. The SMA-HI provides an opportunity for researchers and clinicians to measure a SMA patient's perception of their health and determine relevant changes in response to therapeutic intervention or disease progression.