Eosinophilic Granulomatosis with Polyangiitis Presenting with an Acute Hypersensitivity Pneumonitis-like CT Pattern: A Case Report.

The patient was a man in his 20s with a history of childhood asthma who presented with fever and dyspnea. Chest CT revealed diffuse bilateral centrilobular ground-glass opacities, and a history of environmental exposure suggested acute hypersensitivity pneumonitis (HP). However, bronchoalveolar lavage revealed marked eosinophilia (75%), and a transbronchial lung biopsy demonstrated small vessel vasculitis with eosinophilic infiltration. Combined with negative anti-neutrophil cytoplasmic antibodies (ANCA), ANCA-negative eosinophilic granulomatosis with polyangiitis (EGPA) was diagnosed in this patient. Prednisolone (30 mg/day) resulted in rapid improvement, and remission was maintained for 6 months. This case shows that EGPA can mimic acute HP, underscoring the diagnostic value of bronchoscopy and histopathology when eosinophilic inflammation is present.