What is the stepwise investigation of patients suspected of inflammatory myopathy?  

I have published an algorithmic approach to suspected inflammatory myopathy in Continuum Lifelong Learning in Neurology from AAN (Manousakis, PMID 36537973). Unfortunately, the article is not free, and I can't attach the algorithm in this response, because it's a PPT file. Happy to provide it upon r...

If clinical suspicion is high, you can also consider sending MyoMarker 3 in addition to MRI and biopsy, as Dr. @Aggarwal recommends.

MRI followed by muscle biopsy.

Diabetic myopathy, colchicine-induced neuromyopathy, and statin-induced necrotizing myopathy can be irreversible even when the drug is withdrawn, especially in patients with positive anti-HMG CoA reductase antibodies.

Remember alcoholic myopathy as well.