The modified Spinal Muscular Atrophy Functional Rating Scale (SMAFRS) is a psychometrically stable and unidimensional outcome measure, even though certain items are misfitting like those related to respiratory and bulbar function. This is according to a new study published in the journal Muscle and Nerve by researchers from the US.

“Overall, the modified SMAFRS is a psychometrically reliable tool in assessment of adult patients with SMA,” the study authors concluded.

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The SMAFRS was first developed to detect any changes in patients with SMA over time. The modified version of the scale tests 10 activities of daily living. 

Here, the research team analyzed data from the modified SMAFRS using item response theory psychometric models. They analyzed the responses of 41 adult patients with SMA type 2, 3, or 4 disease some of whom could still walk while others could not.

The results showed that most items on the scale had good fitting. The only exceptions were “toileting” and “respiratory.”

The researchers also reported that most items covered a good range of disabilities. There was only a negligible breach of unidimensionality from “eating,” “dressing,” and “respiratory” items.

The differential item function underlined the differences between patients who could and could not walk in terms of “toileting,” “turning,” “transferring,” “walking,” and “respiratory” items.

According to the authors of the study, the differences “need to be taken into consideration in clinical trial design.”

“Overall, the modified SMAFRS is a psychometrically reliable patient-reported functional outcome measure, which may be used as a primary or secondary outcome measure depending on the clinical study or trial design,” they said.

SMA is a rare neurodegenerative disease characterized by progressive weakness and loss of movement. The disease can negatively affect many aspects of a patient’s life. 


Sadjadi R, Kelly K, Glanzman AM, et al. Psychometric evaluation of modified spinal muscular atrophy functional rating scale (SMAFRS) in adult patients using Rasch analysis. Muscle Nerve. Published online January 5, 2023. doi:10.1002/mus.27785