MX1 and dermatomyositis: In a 138-specimen series, sarcoplasmic MxA showed 46% sensitivity and 94% specificity for DM (perifascicular pattern in all positives), with prior cohorts reporting ~57–77% sensitivity and 98–100% specificity; recent guidance therefore recommends adding MxA to standard biopsy panels while interpreting results alongside morphology to avoid pitfalls [40,41].