SUMMARY Churg–Strauss syndrome, Eosinophilic granulomatosis with polyangiitis (EGPA), is a systemic vasculitis that affects small– to medium-sized vessels. It is rare and part of the Anti-neutrophil cytoplasm antibody-associated vasculitis (ANCA) group. We present a 37-year-old man, with a previous history of asthma, that was sent to the ED due to 2 weeks of productive cough, occasional dyspnea on exertion, fever (one week), asthenia, and anorexia. Upon physical examination, he was subfebrile and tachycardic. He had leukocytosis (17.00 x10^9/L) and eosinophilia of 20.0 % (3.4 X10^9/L), creatinine level of 1.5 mg/dL, subtle elevation on liver function tests and CRP of 10.82mg/dL. On Chest X-Ray, there was infiltrate on the right pulmonary base. Due to a strong suspicion of EGPA, he was started on 80mg of prednisolone from admission. ANCA MPO was positive, with the remaining auto-immune study negative. He underwent Thorax CT (under corticotherapy) without relevant changes, as well as bronchoalveolar lavage, without macroscopic signs of alveolar hemorrhage. Because of active urinary sediment, nephrotic proteinuria (6.5g/24h), and acute renal failure he underwent a renal biopsy, which revealed pauci-immune crescentic glomerulonephritis, with predominantly acute findings (in the context of ANCA-MPO Vasculitis – EGPA). After the biopsy, he received three 1g methylprednisolone pulses and was started on Cyclophosphamide. He remained asymptomatic and renal function was restored. This case highlights the importance of integrating all findings in one clinical scenario to prevent a more complex disease diagnosis, with a specific treatment, from being missed.
