Microscopic Polyangiitis

An MPA flare can turn a subtle urine abnormality into kidney failure, or pulmonary capillaritis into life-threatening alveolar bleeding. The bedside pattern to catch is injury in more than one small-vessel organ—especially new glomerular bleeding alongside hypoxaemia, diffuse infiltrates, or an unexplained haemoglobin fall. Visible haemoptysis is helpful when present, but its absence cannot clear the lungs. MPA is usually MPO-ANCA-associated and lacks granulomatous inflammation. The diagnostic task is to match serology or tissue to the clinical syndrome, while the management task is to decide whether organ damage is already threatening life or irreversible function. That distinction determines the speed of glucocorticoid and immunosuppressive treatment, the need to consider plasma exchange, and the intensity of toxicity and infection surveillance.