Dents are not typically contributed to muscle atrophy but fat loss! Muscles are long, not small little dents. It would not point to ALS!
The muscle sits underneath fat. Fat is what is directly underneath the skin. Anyone who has had a muscle biopsy knows how far down muscle is.
Atrophy does not happen really quickly unless someone is really sedentary or bed bound. Does that describe you?
If a person with MG does not or cannot exercise, atrophy will occur. No, it is not a primary symptom of MG, but it can be a secondary one.
How large are the dents? Where?
Perhaps you could get a second opinion from another neuro. Have you seen an endocrinologist? What about a physical therapist to access your muscles?
I don't know what else to tell you. It'll be hard to diagnose anything now that you are on Pred!
Annie