Muscle ultrasound helps assess SMA in children treated with approved drug
Study: Patients showed muscle wasting linked to functional impairments
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- Muscle ultrasound effectively assesses muscle health in children with SMA.
- Children with SMA show muscle wasting and fat/connective tissue accumulation.
- Ultrasound links muscle structure to motor function in SMA patients on Spinraza.
Muscle ultrasound helps assess muscle health and its association with motor function in children with spinal muscular atrophy (SMA) treated with Spinraza (nusinersen), according to a recent study.
While the findings varied by muscle group and SMA type, ultrasound data generally indicated that children with SMA exhibited muscle wasting and signs of fat and connective tissue accumulation. These changes were associated with functional impairments.
According to researchers, this study shows that “quantitative muscle ultrasonography provides a feasible and objective approach for assessing muscle structure in relation to functional status in children with SMA receiving disease-modifying therapy.”
The study, “Quantitative Ultrasonographic Assessment of Muscle Structure and Correlations with Motor Function Scales in Nusinersen-Treated Children with Spinal Muscular Atrophy,” was published in the Archives of Physical Medicine and Rehabilitation.
Muscle ultrasonography uses sound waves to generate images of tissue
SMA is typically caused by mutations in the SMN1 gene that result in no to low production of the survival motor neuron (SMN) protein. This leads to the progressive loss of motor neurons, the specialized nerve cells responsible for movement control, and subsequent muscle weakness and wasting.
Muscle ultrasonography uses sound waves to generate images of tissue. This technique can help assess muscle size and health. Previous studies demonstrated that muscle abnormalities in ultrasound imaging are associated with motor function in people with SMA.
“Muscle ultrasonography … offers a non-invasive, repeatable, and practical tool for assessing muscle structure, with minimal dependence on patient cooperation and the ability to evaluate multiple muscle groups rapidly,” scientists from Turkey wrote.
In this study, they used muscle ultrasound to specifically assess changes in muscle structure in children with SMA treated with Biogen‘s Spinraza and their association with motor function scores.
SMA children had significantly lower muscle thickness
The study included 34 children with genetically confirmed SMA and 34 age- and sex-matched healthy controls. Children with SMA had a mean age of 7 years at study enrollment and were being treated with Spinraza for about three years on average. Among the patients, 15 had SMA type 1, 11 had SMA type 2, and eight had SMA type 3.
All underwent ultrasound testing of different muscles, including the biceps brachii (upper arm), forearm flexors (lower arm), quadriceps femoris (thigh), and tibialis anterior (lower leg).
For all examined muscle groups, SMA children had significantly lower muscle thickness and higher echointensity values than healthy children. Low muscle thickness indicates loss of muscle tissue, while higher echointensity indicates that healthy muscle tissue has been replaced by fat or connective tissue.
Still, the findings for specific muscle groups and SMA types varied. Type 1 patients showed significant differences in all analyzed muscles compared with healthy children, while type 2 children showed no differences in the upper arm, and type 3 children only showed differences in the thigh.
[These findings] extend previous work by demonstrating clinically meaningful associations between quantitative muscle ultrasonography and functional status in treated patients.
The functional status of type 1 children was assessed using the Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND), whereas all other patients were evaluated with the Hammersmith Functional Motor Scale Expanded (HFMSE). The Revised Upper Limb Module (RULM) was used to evaluate upper limb function in patients older than 2 years who were able to sit independently.
CHOP-INTEND and HFMSE scores were significantly associated with forearm and lower leg muscle sizes. Worse scores in both of these motor function measures were also associated with higher echointensity in muscle, particularly in the lower leg.
Higher (better) RULM scores, conversely, correlated with thicker arm muscles. In the upper arm, higher echointensity values were associated with lower RULM scores.
According to the researchers, these findings “extend previous work by demonstrating clinically meaningful associations between quantitative muscle ultrasonography and functional status in treated patients.”
As study limitations, they noted that since the analysis was done at a single point in time, it wasn’t possible to track how muscles change over time. Also, treatment duration was variable.
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