Remission and low disease activity definitions in adult idiopathic inflammatory myopathies: A narrative review by myositis clinical trials consortium (MCTC).

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of rare systemic autoimmune rheumatic diseases. Despite advances in treatment, the definition of remission and low disease activity (LDA) in IIM remains inconsistent and lacks consensus and validation. This review summarizes existing published definitions, achievement rates, and predictive factors of remission/LDA in adult IIM, focusing on dermatomyositis (DM), polymyositis (PM), anti-synthetase syndrome (ASyS), and immune-mediated necrotizing myopathies (IMNM). Our literature review revealed a wide variability in remission definitions, incorporating physician assessment, muscle strength, laboratory normalization, and medication tapering or discontinuation. Some studies defined "remission on medication", while others required complete treatment cessation. Most definitions required a minimum duration of six months. Organ-specific remission (including for the skin, lung, and muscle domains) was inconsistently addressed. LDA has been less extensively studied in IIM, with the myositis disease activity assessment visual analog scales (MYOACT) being the only measure applied to DM. Remission rates varied widely, with stricter criteria yielding lower rates. Factors associated with remission included younger age, early immunosuppressive treatment, non-severe muscle involvement, the absence of myositis-specific autoantibodies (MSA), although some studies reported positivity for certain MSA were associated with remission. Conversely, remission was less likely for patients with PM, overlap myositis, and those positive for anti-TIF1-γ or Ku autoantibodies. Standardized remission criteria incorporating physician assessment, patient assessment, organ-specific parameters, laboratory assessments, and sustained remission duration are essential for harmonizing clinical and research evaluations in IIM. Establishing uniform definitions will improve therapeutic outcome assessments and facilitate meaningful comparisons in clinical trials and real-world practice.