Rasch Analysis of the Motor Function Measure in Patients With Congenital Muscle Dystrophy and Congenital Myopathy

Abstract

Objectives To monitor treatment effects in patients with congenital myopathies and congenital muscular dystrophies, valid outcome measures are necessary. The Motor Function Measure (MFM) was examined for robustness, and changes are proposed for better adequacy. Design Observational study based on data previously collected from several cohorts. Setting Nineteen departments of physical medicine or neuromuscular consultation in France, Belgium, and the United States. Participants Patients (N=289) aged 5 to 77 years. Interventions None. Main Outcome Measures A Rasch analysis examined the robustness of the MFM across the disease spectrum. The 3 domains of the scale (standing position and transfers, axial and proximal motor function, and distal motor function) were independently examined with a partial credit model. Results The original 32-item MFM did not sufficiently fit the Rasch model expectations in either of its domains. Switching from a 4- to a 3-category response scale in 18 items restored response order in 16. Various additional checks suggested the removal of 7 items. The resulting Rasch-scaled Motor Function Measure with 25 items for congenital disorders of the muscle (Rs-MFM25CDM) demonstrated a good fit to the Rasch model. Domain 1 was well targeted to the whole severity spectrum—close mean locations for items and persons (0 vs 0.316)—whereas domains 2 and 3 were better targeted to severe cases. The reliability coefficients of the Rs-MFM25CDM suggested sufficient ability for each summed score to distinguish between patient groups (0.9, 0.8, and 0.7 for domains 1, 2, and 3, respectively). A sufficient agreement was found between results of the Rasch analysis and physical therapists’ opinions. Conclusions The Rs-MFM25CDM can be considered a clinically relevant linear scale in each of its 3 domains and may be soon reliably used for assessment in congenital disorders of the muscle.

Motor function performance in individuals with RYR1‐related myopathies

“…Participants in this study exhibited the greatest difficulty performing activities in the standing and transfers domain (D1), whereas axial (D2) and distal (D3) motor functions were mostly preserved. These results are consistent with findings described in a report of a larger study that included individuals with congenital myopathies and congenital muscular dystrophies, in which D1 was also the most affected in congenital myopathies in general . This finding contrasted with those of individuals with muscular dystrophy, who presented with a greater mobility limitation, namely 40% of the possible D1 score, and who declined in D1 score over 3 months .…”

Correlation of phenotype with genotype and protein structure in RYR1-related disorders

“…Motor function was evaluated using MFM-32 which has been developed and validated for use in the neuromuscular disease population, including RYR1 -RD [80, 81]. This was completed for each participant by physical therapists.…”

Upper extremity outcome measures for collagen VI-related myopathy and LAMA2-related muscular dystrophy

“…All upper extremity measures used in this study were correlated with the Motor Function Measure 32 (MFM32). The MFM32 evaluates head, trunk, upper and lower limb function in both ambulatory and non-ambulatory individuals, is reliable, and has been validated in individuals with CMD [6,7,10]. In addition to the Jebsen, the battery of upper extremity assessments included the Quality of Upper Extremity Skills Test (QUEST), hand held dynamometry, goniometry, and MyoSet Tools.…”