To preliminarily assess the efficacy and safety of efgartigimod in patients with refractory idiopathic inflammatory myopathy (IIM), with particular attention to improvements in clinical and functional outcomes and the occurrence of treatment-emergent adverse events during follow-up.

This retrospective study included eight consecutive patients with IIM who were diagnosed and treated at our center between August 2024 and July 2025. The study population comprised two patients with immune-mediated necrotizing myopathy, five with antisynthetase syndrome, and one with anti-MDA5 dermatomyositis, thereby covering several major IIM subtypes encountered in routine clinical practice. Among the eight patients, seven had interstitial lung disease (ILD) confirmed by high-resolution computed tomography, indicating a high prevalence of pulmonary involvement in this cohort. All patients received intravenous efgartigimod at a dose of 10 mg/kg once weekly for four consecutive weeks as add-on therapy to their existing treatment regimens, which consisted of glucocorticoids in combination with immunosuppressive agents. Clinical data were collected retrospectively from the time of hospital admission through the last follow-up visit. Baseline demographic and clinical characteristics were documented, and treatment response was assessed using the ACR/EULAR core set measures, including physician global assessment (PhGA), patient global assessment (PtGA), Health Assessment Questionnaire (HAQ), Myositis Disease Activity Assessment Tool (MDAAT), Manual Muscle Testing-8 (MMT-8), serum creatine kinase (CK) levels, and prednisone dose. In addition, HRCT findings were serially evaluated using the Warrick score to assess changes in pulmonary involvement. Safety was evaluated throughout the observation period, and all adverse events were recorded to characterize the tolerability of efgartigimod in this refractory IIM cohort.

Eight patients with refractory IIM received intravenous efgartigimod at a dose of 10 mg/kg weekly as an add-on to standard therapy. Seven patients achieved clinically meaningful improvement according to ACR/EULAR response criteria, whereas one patient with immune-mediated necrotizing myopathy and a prolonged disease duration of 116 months did not demonstrate significant benefit, suggesting that long-standing disease may limit therapeutic response.Among responders, both physician- and patient-reported measures of disease activity improved substantially. Functional status, assessed using the HAQ, improved from a median of 1.85 (IQR 0.98) at baseline to 0.60 (IQR 0.33) at six months, corresponding to a 67.6% reduction (P < 0.001). Muscle strength, evaluated by MMT-8, increased from a median of 63.75 (IQR 13.13) to 120.5 (IQR 18.08), reflecting an 89.0% improvement (P < 0.001). These findings indicate marked recovery of both functional ability and muscle performance following treatment.Seven patients had concomitant ILD. Pulmonary involvement, quantified using the Warrick score, improved from a median of 6.0 (IQR 1.25) to 2.5 (IQR 1.50), corresponding to a 58.3% reduction (P < 0.005), suggesting radiographic improvement or stabilization of ILD. No adverse events were reported during the treatment and follow-up period, indicating a favorable tolerability profile.Notably, one anti-MDA5-positive patient with progressive ILD despite prior treatment with glucocorticoids, a JAK inhibitor, and tacrolimus demonstrated partial resolution of cervicothoracic and mediastinal emphysema and complete resolution of anterior chest wall subcutaneous emphysema following a single dose of efgartigimod. ILD stabilized, and the patient achieved marked overall clinical improvement after completing the full treatment cycle.Collectively, these data suggest that efgartigimod provides rapid and clinically meaningful improvements in muscle strength, functional status, and pulmonary outcomes in patients with refractory IIM, including those with high-risk ILD and anti-MDA5 positivity, while maintaining a favorable safety profile.

 Efgartigimod demonstrated encouraging therapeutic efficacy in patients with refractory IIM, including those with concomitant ILD. Clinical improvement was observed across multiple disease activity and functional outcome measures, accompanied by a reduction in glucocorticoid requirements without evidence of disease worsening. Notably, pulmonary involvement remained stable or improved in patients with ILD, further supporting its potential benefit in this high-risk subgroup. Collectively, these findings suggest that efgartigimod may offer a clinically meaningful steroid-sparing effect while maintaining overall disease control. Although preliminary, the present results support efgartigimod as a promising therapeutic option for refractory IIM and warrant further investigation in larger prospective studies.