Purpose <p>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.</p> Methods <p>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.</p> Results <p>Whole-lung SUVmax was significantly higher in MDA5⁺DM patients (3.32 vs. 0.67, <i>p &lt;</i> 0.0001), with left lower lobe showing the most prominent difference (<i>p</i> = 0.0003). SUVmax strongly correlated with HRCT inflammation/fibrosis indices (e.g., left lower lobe vs. PII at 3 months: <i>r</i> = 0.9863, <i>p &lt;</i> 0.0001) and small-to-medium airway function (lung vs. MMEF 75/25: <i>r</i>=-0.8168, <i>p</i> = 0.0133). Baseline SUVmax predicted 3–12-month lesion progression and lung function changes, with deceased patients having higher baseline whole-lung SUVmax (<i>p</i> = 0.008).</p> Conclusion <p>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.</p> Graphical abstract <p></p>