Do you routinely perform muscle biopsies in patients presenting with the classic symptoms of Inclusion Body Myositis along with positive CN1A antibody?

YES. There are new consensus guidelines from ENMC about the diagnosis of IBM (Lilleker et al., PMID 38522330). They define the clinical presentation of IBM as typical (age >45, progression over >12 months, long finger flexor weakness > deltoid weakness, quadriceps weakness > hip flexors), or atypical (onset with dysphagia, asymptomatic hyperCKemia, facial diplegia, trunk weakness, etc.).

Whether the presentation is typical or atypical, a mandatory criterion for diagnosis is the presence of endomysial inflammation on muscle biopsy. Supportive criteria include:

1. additional muscle biopsy findings (rimmed vacuoles, amyloid or other protein deposition, mitochondrial abnormalities),
2. positive CN1A antibody, or
3. imaging findings (characteristic muscle...