A couple of days ago, I complained about the lack of publications on ALS metabolism in skeletal muscles, which represent only a tiny fraction of the huge number of ALS (mostly useless) publications.
Here is one article describing the evolution of the masseter muscle, one of the muscles of mastication, during the disease course in a SOD1 mice model.
Why study the masseter muscle in ALS? Because it is one of the few skeletal muscles that is not affected by the disease.
The authors observed that, despite a decrease in limb motor functions, the feeding function of these mice was preserved until the late stages of the disease. Remarkably, the masseter muscle showed no reduction in muscle volume, wet weight, or muscle fiber cross-sectional area. Furthermore, no changes were observed in muscle fiber types, indicating a possible resistance of the masseter muscle to ALS-induced impairment. A potential reason for the lack of atrophy in the masseter muscle could be its higher number of muscle satellite cells compared to that of the gastrocnemius muscle. This abundance may promote the maintenance of muscle fiber nuclei, thereby contributing to muscle tissue regeneration.
What they are saying in the background is: * Something is stressing the skeletal muscles in ALS, which looks quite a reasonable assumption to me. * Maybe it would be possible to design an ALS therapy targeting muscle satellite cells. This looks less likely to me.
While the authors promote the idea that the disease may, at least partly, start in muscles, I can't help myself thinking that maybe the reason it is preserved is simply that this muscle (as for eye movements) is activated by the trigeminal nerve which is usually preserved in ALS.
It seems to me that in spinal ALS, the longer motoneurones fail early (hands, feet) and the shorter ones survive longer. Indeed in bulbar ALS, the situation is reversed, but ALS mice models attempt only to model spinal ALS. So in my opinion, the authors should have considered that the lack of wasting of mice's masseter muscle may stem from a still functioning trigeminal nerve.