Steroid-Free Remission of Eosinophilic Granulomatosis With Polyangiitis Achieved With Low-Dose Mepolizumab: A Case Report.

A 73-year-old man with a history of severe asthma was admitted to our hospital with progressive dyspnea, weight loss, polyarthralgia, and myalgia. Laboratory tests revealed peripheral eosinophilia and anti-myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA) negativity. Chest computed tomography revealed diffuse ground-glass opacities, interlobular septal, and bronchial wall thickening, suggesting eosinophilic pulmonary infiltration. Based on this clinical presentation and the ACR/EULAR 2022 classification criteria, as well as the Japanese Ministry of Health, Labour and Welfare criteria, eosinophilic granulomatosis with polyangiitis (EGPA) was diagnosed. However, the patient declined treatment with glucocorticoids owing to concurrent diabetes mellitus; therefore, subcutaneous low-dose (100 mg/month) mepolizumab monotherapy was initiated as an alternative strategy, with the lower dose specifically selected to alleviate the patient's financial burden. Notably, a rapid decrease in eosinophil counts was observed within just 4 days of administration, and remission was achieved and maintained for 2 years. In conclusion, this case suggests that mepolizumab monotherapy may be a viable option for certain patients with non-severe, MPO-ANCA-negative EGPA who cannot tolerate standard high-dose glucocorticoid therapy or have financial constraints.