Flares and definition of worsening in inflammatory myopathies: a narrative review of the literature.

Idiopathic inflammatory myopathies (IIMs) follow a chronic, polycyclic course in a substantial proportion of patients. Unlike remission, which has recently been standardized, the definition of flare (or worsening) remains highly heterogeneous, creating a divide between clinical trials and real-world practice. Validated core set definitions of worsening exist for trials but were derived by consensus on paper patient profiles and are criticized for inadequate content validity; observational studies instead rely on simplified markers such as enzyme elevation or therapeutic escalation. This review summarizes existing definitions, contrasting the International Myositis Assessment and Clinical Studies Group and Paediatric Rheumatology International Trials Organisation statistical criteria with the variable definitions used in longitudinal cohorts. We examine reported flare rates and predictors, the discordance between global and organ-specific (skin, muscle, lung) worsening, and the lessons offered by flare definitions in other rheumatic and inflammatory diseases. We then propose a multi-domain, treatment-anchored framework intended to bridge statistical rigour and clinical utility.