New Technique Found Suitable for Body Composition Measures in SMA

Marisa Wexler MS avatar

by Marisa Wexler MS |

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A technique called bioelectrical impedance analysis (BIA) can be used to measure body composition in people with type 2 or 3 spinal muscular atrophy (SMA), a new study reports.

The study, “A comparative analysis of body composition assessment by BIA and DXA in children with type II and III spinal muscular atrophy,” was published in Frontiers in Neurology.

Measuring body composition — the amount of body mass that’s made up of fat, muscle, and so on — is essential to help manage care and nutrition for people with SMA.

A technique called dual-energy X-ray absorptiometry, or DXA, is described in the study as the generally regarded “gold standard” for assessing body composition. In DXA, body tissue is assessed using X-rays.

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BIA is an alternate technique that involves measuring how electricity moves through body tissue. Compared with DXA, BIA offers some logistical advantages — it doesn’t expose patients to X-ray radiation, and it’s easier to perform on patients with abnormalities in physical development like scoliosis (sideways curving of the spine), a common symptom of SMA.

Also, “DXA has limitations because it is not portable and expensive and frequently requires training and operation by licensed technicians because of the small amount of potential radiation exposure,” the researchers wrote.

Studies in the general population have shown that DXA and BIA measures are generally consistent with each other. However, there has been minimal research comparing these techniques in people with neuromuscular diseases like SMA.

The study and its results

To learn more, researchers in China compared DXA and BIA measures recorded for 57 children with SMA followed at a single center in China between 2019 and 2021.

“This present study compared the concordance between the BIA device and the current gold-standard DXA device on the measurement of body composition in children with SMA for the first time,” the team wrote.

Among the children included in the study, 27 had type 2 SMA, while the other 30 had type 3 disease. Most of the type 2 patients could sit independently, and most of the type 3 patients could walk.

Results showed that, compared with DXA measurements, BIA tended to underestimate fat mass by about 12.6% on average. Conversely, BIA overestimated muscle mass by 11.9% on average.

BIA also overestimated bone mineral content by an average of 50%, and it overestimated visceral fat area — an assessment of “hidden” fat that is stored deep in the abdomen and wrapped around organs — by about 77.6%.

“Overall, the difference between [muscle mass] … and [fat mass] … measured by DXA and BIA was minor, whereas the difference between [visceral fat area] … was significantly large,” the researchers wrote.

Despite these differences, statistical tests showed that overall measures, and particularly measures of fat mass and muscle mass, generally showed good agreement between the two measurement techniques. The results indicated that the agreement was generally better in patients with type 3 disease compared with those with type 2.

Collectively, the results indicate that “BIA could be considered as a portable, simple-to-use, and appropriate method for body composition measurement to guide clinical nutritional assessment in patients with SMA, particularly when measuring” muscle mass and fat mass, the researchers wrote, adding that these measures are “of vital importance for assessing the nutritional status of children with SMA.”

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