B23-15 Structure-function Coupling and Quantitative Imaging Biomarkers in Polymyositis Dermatomyositis Associated Interstitial Lung Disease

Abstract Rationale Polymyositis and dermatomyositis-associated interstitial lung disease (PM/DM-ILD) exhibits heterogeneous inflammatory and fibrotic patterns. The relationship between quantitative CT (qCT)-derived structural measures and physiological progression in this disease remain uncertain. Defining this structure-function coupling may improve disease monitoring and endpoint selection in clinical trials. Methods Patients with PM/DM-ILD were identified from a global imaging repository and two UK healthcare trusts. Volumetric evaluation of the airways, pulmonary vessels and parenchymal patterns, ground glass opacification and fibrosis were quantified using Qureight’s deep learning-based qCT models, Air8™, Vascul8™, Glass8™, and Fibr8™, respectively, normalised against total lung volume. Annualised change in percent-predicted forced vital capacity (ΔppFVC%) and fibrosis (%Fibr8) were estimated using linear mixed-effects models from longitudinal spirometry. Associations between baseline CT biomarkers, fibrosis progression, and imaging sub-compartments (airway, vascular, ground-glass) with ppFVC were assessed by linear regression. Results Sixty-two patients were included (mean age 58.6±13.3 years; 56% female). Baseline fibrosis averaged 14.6±11.1%, and baseline ppFVC 72.6±20.3%. Baseline fibrosis correlated with baseline ppFVC (β = -0.65±0.22, p = 0.005) but did not predict subsequent FVC decline (β =-0.24±0.17, p = 0.17). Fibrosis progression was significantly associated with FVC decline (β = 0.043±0.016, p = 0.009). Baseline ground-glass opacification volume showed a non-significant trend toward association with FVC decline (β = -0.64±0.36, p = 0.08), while vascular and airway volumes did not (p = 0.35 and p = 0.82). Conclusions In PM/DM-ILD, baseline fibrosis reflects structural impairment but not future decline, whereas fibrosis progression tracks functional loss. This pattern indicates dynamic structure-function coupling driven predominantly by fibrotic activity, with limited inflammatory contribution and minimal vascular or airway influence. Quantitative CT biomarkers may therefore provide complementary sensitivity for assessing disease activity and therapeutic response in myositis-related interstitial lung disease. This abstract is funded by: None