Analysis Shows Utility of Tool to Detect Motor Function Change in SMA

Findings from a recent analysis offer evidence of an assessment tool's measurement properties when used to evaluate motor function in patients with spinal muscular atrophy (SMA).

The 32-item Motor Function Measure (MFM32) has been evaluated in a broader category of neuromuscular diseases, but researchers in this study wanted to evaluate it specifically in SMA. MFM32 assesses motor function across 3 categories: standing, transfers, and ambulation; proximal and axial function; and distal function.

Drawing on data from 110 patients with type 2 or non-ambulant type 3 SMA being treating with olesoxime or placebo in a Phase 2 study, the researchers found that the assessment is a valid, reliable, and responsive assessment of motor function ability for these patients.

“Valid and reliable measures of SMA-related outcomes allow for a better understanding of the natural history of all SMA types and of subgroups of disease trajectory,” wrote the researchers. “Additionally, assessment which are sensitive to change and measure symptoms and outcomes that are meaningful to individuals with SMA are essential for assessing therapeutic strategies to treat SMA.”

The researchers argue these findings support the use of MFM32 in longitudinal studies of patients with type 2 or non-ambulant type 3 SMA.

According to the researchers, all analyses performed to test the reliability of MFM32 achieved met the acceptable threshold of >0.7. These analyses specifically showed the assessment’s reliability by high intraclass correlation coefficient (ICC)—test-retest reliability—with an ICC of 0.93 in patients classified as “no change” on Clinician Global Impression of Change, and an ICC of 0.95 in patients classified as “no change” on Patient/Parent Global Impression of Change. The analyses also showed a high Cronbach’s α—internal consistency.

While MFM32 scores at baseline showed strong correlation with both Hammersmith Functional Motor Scale (HFMS) and forced vital capacity (FVC) scores, the correlation seen between MFM32 and HFMS (Spearman’s ρ = 0.87, P <.0001, N = 110) was greater than that seen between MFM32 and FVC (Spearman’s ρ = 0.61, P <.0001, N = 104), demonstrating convergent validity.

Meanwhile, the known-groups validity analyses revealed that least square (LS) means had expected patterns, such as larger MFM32 scores for patients with less severe disease, for HFMS score at screening (LS mean difference = 17.4), ability to stand (LS mean difference = 16.5), and ability to sit (LS mean difference = 11.9). The researchers noted that all analyses performed showed significant differences between groups.

Changes in global condition, as assessed by both clinician-rated and patient-/parent-rated change in global health, was also able to be detected by MFM32. The researchers highlighted that significant differences in LS mean change scores were observed between groups, using both anchors, with MFM32 scores having expected patterns, such as worsening in the “minimally worse” or worse groups and small improvements in the “no change” or better groups.

“Despite the majority of patients being rated as ‘no change’ on both the CGI-C and PGI-C, the MFM32 was still able to detect significant differences between those classified as stable or improving and those classified as worsening, as defined by these anchor scales,” wrote the researchers.

Reference

Trundell D, Le Scouiller S, Le Goff L, Gorni K, Vuillerot C. Assessment of the validity and reliability of the 32-item Motor Function Measure in individuals with Type 2 or non-ambulant Type 3 spinal muscular atrophy. PLoS One. Published online September 18, 2020. doi:10.1371/journal.pone