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Ultrasound Measures of Muscle May Help in Diagnosing, Evaluating ALS

Measurements taken of muscle using ultrasound could be useful in diagnosing or managing amyotrophic lateral sclerosis (ALS), a small study suggests.

The study, “Application of Muscle Ultrasound for the evaluation of Patients with Amyotrophic Lateral Sclerosis: An observational Cross‐Sectional Study,” was published in Muscle & Nerve. Ultrasound is a technique that uses sound waves to easily visualize things within the body. Muscle ultrasound can provide useful measures, such as a muscle’s thickness or echo intensity. High echo intensity is thought to be indicative of increased fat and/or scar tissue in muscles, generally indicative of poorer muscle health.

However, it isn’t fully understood how ultrasound measurements reflect muscle functionality. For instance, it’s unclear whether any parameter measured via ultrasound is associated with motor unit number index (MUNIX), which essentially records how many nerves are sending signals to a muscle, and can be used to estimate the rate of disease progression in ALS patients.

Researchers used muscle ultrasound to evaluate 18 people with ALS (14 sporadic, four familial) and 18 people without ALS (controls). The two groups were matched in terms of age (early 50s, on average) and sex distribution (slightly more males than females). All were right-handed.

Three different muscles — two in the legs/feet and one in the hand — were evaluated. Then, researchers compared ultrasound measurements between the groups and looked for associations with other parameters, such as MUNIX. While no differences in ultrasound-measured muscle thickness between the groups were found, echo intensity for all measured muscles was significantly higher in the ALS group than in the control group. Multiple measures of muscle function — including manual muscle testing (MMT) score — were significantly poorer in ALS patients than controls.

“Our results showed that compared to the control group, ALS patients had significantly increased EI [echointensity] values,” the researchers wrote, adding that this is likely because muscle tissue is replaced with fatty tissue as the disease progresses and motor neurons die.

In statistical models, muscle thickness was not associated with any functional measurement, including MUNIX. However, echo intensity significantly correlated with MUNIX scores for two of the three individual muscles — abductor pollicis brevis (a hand muscle), and tibialis anterior (a muscle in the calf/foot) — and for the three taken together.

Some other echo intensity scores were significantly associated with other parameters. For example, echo intensity in the tibialis anterior was associated with manual muscle testing scores. “We established that the ultrasound variable EI [echointensity] and the electrophysiological variable MUNIX were significantly correlated with clinical and functional indices in patients with ALS. Moreover, we showed that there was an association between MUNIX score and muscle EI,” the researchers concluded.

These results suggest that ultrasound measures could have diagnostic and prognostic value in ALS. The researchers noted, however, that their study is limited by its small sample size, the fact that only a one-time point was assessed, and that it only evaluated ALS.

“Future longitudinal studies with greater sample sizes can overcome these shortcomings,” the researchers wrote, adding, “distinguishing ALS from other neuromuscular diseases should be the next step for these diagnostic techniques.”

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