68Ga-FAPI-04 PET/CT: a new horizon for evaluating pulmonary involvement in MDA5+ dermatomyositis

MDA5 + dermatomyositis (MDA5 + DM) frequently complicates interstitial lung disease (ILD), especially rapidly progressive ILD (RP-ILD), which worsens prognosis. Traditional assessments cannot directly reflect fibroblast activation status, a key driver of pulmonary fibrosis. 68Ga-FAPI-04 PET/CT targets fibroblast activation protein (FAP), but its value in MDA5 + DM remains understudied. Fourteen MDA5 + DM patients and 5 controls were enrolled. 68Ga-FAPI-04 PET/CT was performed to obtain SUVmax of lungs, muscles, and other organs. Clinical data, pulmonary function tests, and deep learning-quantified HRCT indices were collected. Follow-ups for pulmonary function and HRCT were conducted. Correlations between SUVmax, clinical features, and follow-up outcomes were analyzed. Whole-lung SUVmax was significantly higher in MDA5 + DM patients (3.32 vs. 0.67, p < 0.0001), with left lower lobe showing the most prominent difference ( p = 0.0003). SUVmax strongly correlated with HRCT inflammation/fibrosis indices (e.g., left lower lobe vs. PII at 3 months: r = 0.9863, p < 0.0001) and small-to-medium airway function (lung vs. MMEF 75/25: r =-0.8168, p = 0.0133). Baseline SUVmax predicted 3–12-month lesion progression and lung function changes, with deceased patients having higher baseline whole-lung SUVmax ( p = 0.008). This exploratory study suggests that 68Ga-FAPI-04 PET/CT may reflect fibroblast activation and the active inflammatory-fibrotic process, assesses early pulmonary impairments and monitoring lesion progression in MDA5 + DM. It provides a valuable hypothesis-generating tool for clinical evaluation, warranting further validation. Study design, diagnostic imaging patterns, and clinical utility of 68Ga-FAPI-04 PET/CT in MDA5⁺ DM-ILD. The top panel outlines the study workflow. The bottom left panel demonstrates diagnostic efficacy. The bottom right panel highlights monitoring value. MDA5⁺ DM, anti-Melanoma Differentiation-Associated gene 5 positive dermatomyositis; ILD, Interstitial Lung Disease; SUVmax, Maximum Standardized Uptake Value; HRCT, High-Resolution Computed Tomography; FAP, Fibroblast Activation Protein; PII, Pulmonary Inflammation Index; MMEF, Maximal Mid-expiratory Flow.