Juvenile Idiopathic Inflammatory Myopathies.

The juvenile idiopathic inflammatory myopathies (JIIM) are a group of rare, chronic, autoimmune illnesses that affect muscle and, to a lesser extent, skin. The presence of new-onset weakness and, in juvenile dermatomyositis, typical rahes, should lead to consideration of these diagnoses. Careful evaluation to exclude alternative diagnoses is needed. Investigations include a variety of blood tests, imaging, and possibly muscle biopsy. Validated clinical assessments are available for monitoring. Standard treatment includes corticosteroids and methotrexate and often extends beyond 1 year. Outcomes are generally good, but disease persistence remains problematic. Early involvement of providers with expertise in JIIM is essential.