Muscle morphology and intramuscular fat after treatment as usual including BonTA in children with cerebral palsy - a commentary and some context.

Associate Professor Sian Williams

Decreased muscle size (muscle atrophy) and fat infiltration have been believed to be two important muscle changes during the growth of children with cerebral palsy (CP). Muscle atrophy has been well demonstrated in short-term studies in the calf muscle (medial gastrocnemius; MG) in children with CP. However, intramuscular fat infiltration has been less studied, mainly because it has been difficult to measure accurately. Therefore, there is a need for long-term follow-up of muscle alteration, including both muscle structure and composition, in children with CP using a technique that can provide reliable, quantitative, and specific measurement.

In this study, we used different MRI techniques to evaluate muscle composition including intramuscular fat content changes after a 12-month treatment-as-usual (TAU), starting with the first botulinum neurotoxin A (BoNT-A) injection, in children with CP and typically developing peers. All children with CP received at least one injection into the MG. We measured muscle volume, fascicle length, pennation angle, and intramuscular fat fraction of four lower leg muscles, including both muscles that point the foot downward (plantarflexors) and upward (dorsiflexors).

We found that the muscle volume (when adjusted for body size) of all evaluated muscles was not changed after the 12-month TAU in children with CP. Similar results were observed for muscle structure at the fascicle level, including fascicle length and pennation angle. However, the amount of fat within the muscle increased in the MG at the 12-month follow-up.

After a 12-month TAU which involves BoNT-A injection, there was no clear evidence of ingoing muscle atrophy in the lower-leg muscles, including both plantarflexors and dorsiflexors. However, we found increased infiltration of intramuscular fat in the injected muscle (MG), suggesting changes in muscle composition despite stable muscle size.

https://pubmed.ncbi.nlm.nih.gov/42501405/