What aspects on history and physical exam could help differentiate genetic muscular dystrophy from immune-mediated myopathy?

Great question, and one that comes up all the time in clinical practice. Unfortunately, the question gets a little bit complicated because of the heterogeneity of the musculodystrophies, metabolic myopathies, and neuropathies that can mimic myositis (not to mention the phenotypic variation between the different autoimmune myositis subtypes).

For the most part, autoimmune myositis phenotypes will predominantly affect proximal limb musculature (with the notable exception of finger flexor weakness i...