To analyze the clinical manifestations, diagnostic strategies, and treatment options for eosinophilic granulomatosis with polyangiitis (EGPA), and to improve the early recognition and diagnostic capability of eosinophilic granulomatosis with polyangiitis. Additionally, to explore the efficacy of Mepolizumab monotherapy in patients with antineutrophil cytoplasmic antibody (ANCA)-negative eosinophilic granulomatosis with polyangiitis.

A case of antineutrophil cytoplasmic antibody-negative eosinophilic granulomatosis with polyangiitis admitted to our department on July 26, 2024, was selected. The symptoms, signs, laboratory tests, imaging findings, and treatment process were analyzed, and a literature review was conducted.

The patient was a 43-year-old female admitted due to recurrent wheezing and shortness of breath for over 30 years, along with the discovery of a pulmonary shadow for more than one month. She had a medical history of bronchial asthma, chronic sinusitis, and nasal polyps. Auxiliary examinations showed a peripheral white blood cell count of 8.74×10⁹/L, an absolute eosinophil count of 0.90×10⁹/L, an erythrocyte sedimentation rate of 31 mm/1h, and an elevated eosinophil proportion in bronchoalveolar lavage fluid to 76%. Total cholesterol 6.70 mmol/L, LDL cholesterol 3.98 mmol/L, Lipoprotein (a) 344.0 mg/L, Triglycerides 2.64 mmol/L. IgM positive (1.00 COI), IgG significantly elevated (>300.00 AU/ml). Antineutrophil cytoplasmic antibody testing was negative. Pathological biopsy of the right middle lung lobe revealed eosinophil infiltration in the lung tissue. A diagnosis of antineutrophil cytoplasmic antibody-negative eosinophilic granulomatosis with polyangiitis was considered. The patient was treated with Mepolizumab monotherapy for maintenance. Follow-up outpatient examinations showed a decrease in eosinophil count, and chest CT revealed significant absorption of the pulmonary lesions.

Patients with a long-term history of asthma and persistently elevated peripheral blood eosinophil levels should be alert to the possibility of eosinophilic granulomatosis with polyangiitis. Mepolizumab can serve as an effective maintenance treatment for antineutrophil cytoplasmic antibody-negative eosinophilic granulomatosis with polyangiitis.