Abstract Introduction Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare ANCA-associated vasculitis characterized by eosinophilia, asthma, and systemic vasculitis. Renal involvement in EGPA typically manifests as pauci-immune necrotizing glomerulonephritis. Membranous nephropathy is exceedingly rare in this context and may complicate the diagnostic evaluation. We present a diagnostically challenging case of EGPA with biopsy-confirmed membranous nephropathy. Case Presentation A 59-year-old woman with a past medical history of asthma, chronic allergic rhinosinusitis, chronic interstitial lung disease (ILD), common variable immunodeficiency (CVID) on IVIG therapy, and peripheral neuropathy presented with a two-week history of progressive dyspnea on exertion, low-grade fever, and productive cough with greenish expectoration. On presentation, she was febrile(temperature of 100.4 °F), tachycardic (110), and examination revealed weakened dorsiflexion of the left foot. Laboratory workup showed leukocytosis (WBC 11.1 ×109/L) with neutrophilic predominance. Urinalysis revealed 2+ proteinuria, pyuria, and microscopic hematuria. Chest Imaging demonstrated patchy upper lobe opacities and a moderate pericardial effusion. Given her chronic immunosuppressive state secondary to CVID, broad-spectrum antibiotics (vancomycin and cefepime) were initiated. A bronchoalveolar lavage was non-diagnostic, and the infectious workup remained negative. MPO and P-ANCA returned positive raising a suspicion of Eosinophilic Granulomatosis with Polyangiitis. Her foot drop was thought to be vasculitic in nature. Due to concern for a vasculitis, a renal biopsy was performed, revealing mild immune complex-mediated glomerulonephritis with a membranous pattern. PLA2R antibodies were negative, and secondary causes, including systemic lupus erythematosus, hepatitis, NSAID use, and malignancy were excluded. The patient’s respiratory symptoms gradually improved with supportive care, and she was discharged with Pulmonology and Rheumatology follow-up. Post-discharge, she was started on a prednisone taper (initially 60 mg daily) as well as mepolizumab leading to improved eosinophilic disease control. Discussion This patient fulfilled multiple EGPA criteria—eosinophilia, asthma, ANCA positivity, ILD, and neuropathy—yet biopsy revealed MN, a rare renal lesion in EGPA. Renal histology typically shows pauci-immune necrotizing glomerulonephritis, with MN reported only in isolated cases. Exclusion of secondary causes supports a true EGPA-MN association, documented in scattered reports where MN may present as the predominant glomerular lesion. The coexistence of ANCA-mediated vasculitis and immune complex deposition highlights overlapping immunopathologic mechanisms. This case reinforces the diagnostic value of tissue biopsy in systemic vasculitis, especially when clinical and serologic findings are discordant. This case expands the limited literature on MN as an uncommon renal manifestation of EGPA. Recognition of atypical renal patterns is essential, as accurate histopathologic diagnosis guides targeted immunosuppressive therapy and improves outcomes. This abstract is funded by: none
Singh et al. (Fri,) studied this question.