Idiopathic Inflammatory Myositis and Anti-Synthetase Syndrome as Dynamical Multisystem Transitions: Integrating Autoantibody Programs, Organ Coupling, and Progression Trajectories. Conceptual Note — URM / Dynamic Medicine Series.

This Conceptual Note is part of the URM / Dynamic Medicine Series and interprets idiopathic inflammatory myopathy and anti-synthetase syndrome as dynamical multisystem transitions rather than static diagnostic entities. The article integrates autoantibody-defined immune programs, muscle activity, pulmonary involvement, skin and vascular features, biomarker drift, imaging change, and progression trajectories. It focuses particularly on anti-synthetase syndrome as a chronic multisystem coupling disorder and anti-MDA5-positive dermatomyositis as an example of accelerated pulmonary transition through rapidly progressive interstitial lung disease. It proposes that deterioration in IIM and anti-synthetase syndrome may be preceded by measurable system-level dynamical change across immune, muscular, pulmonary, and systemic domains. In this interpretation, autoantibodies, biomarkers, HRCT, pulmonary function, and organ involvement are not only diagnostic or descriptive markers, but temporal signals of disease trajectory. This article forms part of a group of URM / Dynamic Medicine notes interpreting autoimmune and fibro-inflammatory diseases as system-level transitions, trajectories, and coupled multisystem processes, including rheumatoid arthritis flare, systemic lupus erythematosus flare, Sjögren’s disease, CTD-ILD, and idiopathic inflammatory myositis / anti-synthetase syndrome. This work is conceptual and hypothesis-generating. It does not provide clinical treatment recommendations and should not be used to guide individual patient care without appropriate clinical judgment.