ANCA-negative EGPA with migratory pulmonary masses: A case report of mepolizumab response and literature review

Rationale: Eosinophilic granulomatosis with polyangiitis (EGPA) is a small- to medium-vessel vasculitis commonly associated with asthma and eosinophilia. Misdiagnosis as isolated asthma may delay recognition and treatment. Patient concerns: A patient with a long history of asthma presented with persistent respiratory symptoms and a pulmonary mass initially presumed to be asthma-related pathology. Diagnosis: Clinical evaluation, laboratory findings of eosinophilia, and imaging supported the diagnosis of EGPA rather than isolated asthma. Interventions: The patient received glucocorticoid therapy (methylprednisolone) combined with mepolizumab. Outcomes: Treatment resulted in rapid symptomatic improvement and radiological resolution of the pulmonary mass within 1 month. Lessons: This case highlights the diagnostic challenge of distinguishing EGPA from long-standing asthma and supports the role of targeted biologic therapy in achieving effective disease control.