| Sumario: | Background: Microscopic polyangiitis (MPA), a small-vessel antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, may present insidiously with prolonged fever, renal dysfunction, and pulmonary infiltrates--often mimicking infections, especially in tropical settings. Case presentation: A 61-year-old man with longstanding type 2 diabetes, hypertension, and a previous cerebrovascular accident presented with a 3-month history of low-grade fever, exertional dyspnea, fatigue, and pedal edema. He initially received meropenem for pan-resistant Klebsiella urinary infection; later received Helicobacter pylori therapy for gastritis. However, he remained febrile with rising creatinine. On admission, he was tachypneic, hypoxemic, and oliguric, with bilateral lung infiltrates, microscopic hematuria, and anemia (hemoglobin 5.5 g/dl). Infectious workup--including tropical fevers and tuberculosis--were negative. Perinuclear ANCA (P-ANCA) titre >200 U/ml, computerized tomography (CT) lung findings consistent with diffuse alveolar hemorrhage (DAH), and bronchoalveolar lavage positive for hemosiderin- laden macrophages established the diagnosis of MPA. Due to poor renal reserve, the biopsy was deferred. Treatment included intravenous pulse methylprednisolone (1 g/day x 3), three cycles of plasma exchange, and supportive low-efficiency dialysis. He improved clinically, was weaned off oxygen, and transitioned to oral steroids. Conclusion: This case illustrates the diagnostic challenge of MPA presenting as prolonged pyrexia of unknown origin (PUO) with pulmonaryrenal syndrome in a tropical context. After excluding infectious causes, early consideration of ANCA-associated vasculitis and prompt immunosuppressive therapy can be lifesaving.
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