IIM: idiopathic inflammatory myopathy; STIR: short tau inversion recovery; MRI: magnetic resonance imaging; IMNM: immune-mediated necrotizing myositis; SRP: signal recognition particle; HMGCR: 3-hydroxy-3-methylglutaryl-coenzyme A reductase; JDM: juvenile dermatomyositis.
* Muscle strength can be assessed using a standardized manual muscle strength test of 8 muscle groups or an alternative clinical assessment tool of objective measures of muscle strength. Refer to UpToDate topic on diagnosis of JDM and IIM for details.
¶ In addition to assessing for characteristic skin rashes, the fingernail bed is examined by nailfold capillaroscopy to assess for abnormalities consistent with connective tissue disease (eg, nailfold capillary dilatation, tortuosity, dropout [loss of capillary loops], and decreased density).
Δ Additional testing that is performed at the same time to assess for myositis but that is not required for diagnosis includes muscle enzyme levels and STIR sequence MRI.