Thread by @BharatKumarMD

Thanks, Dr. Philippa van Dantzig for such a fascinating case at the Global Meet the Experts (Myositis)!!

#ACR - the experts weigh in: "for these cases, evaluation by a muscle pathologist is really important ... what types of inflammatory cells? muscle fibers? invasion by inflammatory T-cells for instance?"

DDx is really important for this type of pt - DDx should include IBM, Sarcoid, AAV, PM Immuno-mediated necrosis myopathy, Isolated myositis, Paraneoplastic. Dr. GuoChun Wang reemphasizes careful interpretation of the muscle biopsies.

*Isolated vasculitis (not isolated myositis)

Is there any utility in repeating a muscle biopsy?
According to the experts:
- May be helpful, esp if MRI-guided and biopsy is incongruent to clinical features
- Avoid necrotic areas, try to get edematous areas on MRI

Likelihood of paraneoplastic?
According to the experts:
- Necrotizing myositis and rare inflammatory infiltrate would be one sign on biopsy
- Serologies (e.g. TIFF1-gamma, NXP2) can be revealing too

Usefulness of EMG in this setting?
According to experts:
- Not specific for diagnosis so immune tests and biopsies are more important
- May be an indictor of a myopathy (to evaluate motor neurone disease, neuropathies, etc.)

Distal muscle weakness in myositis?
According to experts:
- Sarcoid has multiple forms (acute, chronic progressive, IBM-like) and so that may be potentially consistent
- IBM classically involves finger flexors (and may be much more assymetric than others)
- CK levels may help too