How do you approach selecting optimal muscle biopsy site when evaluating a patient for suspected inflammatory myopathy?

There are a few things to consider when formulating your approach to this, which include 1) the clinical exam, 2) ease of biopsy of muscle, and 3) potential confounders of diagnosis.

The goal is to get a specimen from a muscle that is undergoing active inflammation. These muscles will generally be weak but not completely out. I use the MRC grade 4 as a cut-off, or in other words, the muscle should generate enough force to overcome some resistance. If it can only move against gravity (MRC 3) or worse, then there is a higher chance that the muscle is too far gone, and you'll get a non-specific finding of fatty replacement and muscle atrophy. If there is significant visible atrophy of the muscle, it's also probably too far gone. If you are con...

EMG or MRI.