A patient with a typical clinical presentation of IMNM (muscle weakness, high levels of CPK) and positive anti-HMGCR antibodies leaves no question regarding the diagnosis, and muscle biopsy would not change management. I would reserve muscle biopsy for atypical cases (for example, positive anti-HMGC...

I absolutely agree with Dr. @Eleni Tiniakou. As an additional thought, you may find a muscle biopsy is sometimes useful in selected cases as an additional data-point to guide treatment decisions. For instance, in an IMNM patient with significant atrophy, it may be difficult to assess the degree of a...