Case Report: From misdiagnosis to successful treatment using mepolizumab in ANCA-negative severe EGPA-clinical lessons in eosinophil-targeted therapy.

This paper presents the complex diagnostic course and treatment of a 33-year-old female patient with anti-neutrophil cytoplasmic antibodies (ANCA)-negative eosinophilic granulomatosis with polyangiitis (EGPA). The patient initially presented with asthma and chronic rhinosinusitis. After treatment with omalizumab and glucocorticoids, she progressed to severe EGPA with multi-organ involvement. Following discontinuation of omalizumab and initiation of mepolizumab (300 mg every 4 weeks), her symptoms resolved, and glucocorticoids were tapered. This case suggests that mepolizumab could be effective for inducing and maintaining remission in ANCA-negative severe EGPA with multi-organ involvement. Exposure to omalizumab in undiagnosed EGPA may either mask or unmask disease progression. Clinicians should carefully evaluate for EGPA before initiating biologic therapy in patients with asthma. Furthermore, we successfully extended the mepolizumab dosing interval to 8 weeks with sustained remission, providing preliminary, hypothesis-generating evidence that interval extension of MEP may be considered as a potential de-escalation strategy for maintenance therapy in stable EGPA.