Quantitative magnetic resonance imaging (qMRI) is feasible to map disease states in the upper arm muscles of patients with spinal muscular atrophy (SMA), according to the results of a study published in NMR in Biomedicine

qMRI is already frequently used to map disease states and progression in the leg muscles in SMA, but there is almost a complete lack of data on the arm muscles, which are very important for meaningful activities of daily living.

In the present study, a team of researchers from the Netherlands led by W. Ludo Van Der Po, curator of the Dutch SMA registry, used quantitative assessment of fat fraction, diffusion indices, and water T2 relaxation times to assess disease states in the upper arm muscles of patients with SMA compared to controls. They then related these measures to muscle force.


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The researchers analyzed a total of 13 patients with SMA and 15 controls. They found that fat fraction was significantly higher in the upper arm muscles of patients with SMA compared to controls. This increase negatively correlated with muscle force.

Moreover, the fat fraction was distributed heterogeneously within the triceps brachii and brachialis muscle but not in the biceps brachii muscle. 

There were significant differences between patients with SMA and controls in terms of diffusion indices and water T2 relaxation times. However, there was a slight reduction in mean diffusivity and eigenvalue 1 and 3 in the triceps brachii of patients with SMA. Mean diffusivity positively correlated with muscle force in the triceps brachii. 

“The variation in fat fraction further substantiates the selective vulnerability of muscles,” the researchers wrote. “The reduced [diffusion tensor imaging] indices along with the positive correlation of [mean diffusivity] with muscle force point to myofiber atrophy.”

More research is necessary to better understand the use of qMRI to map the progression of SMA and explore the effects of different therapies, the researchers said.

Reference

Hooijmans MT, Habets LE, van den Berg S, et al. Multi-modal MR imaging of the upper arm muscles of patients with spinal muscular atrophy. NMR Biomed. Published online January 20, 2022. doi:10.1002/nbm.4696