Granulomatosis With Polyangiitis (GPA)

Granulomatosis with polyangiitis (GPA) is an ANCA-associated small-vessel necrotising vasculitis. It is usually associated with antibodies against proteinase 3 (PR3-ANCA), although myeloperoxidase (MPO-ANCA) can also occur. The antibody is not simply a laboratory marker. ANCA can activate primed neutrophils, which adhere to the endothelium and release oxidants and proteolytic enzymes. The resulting injury targets capillaries, arterioles, and venules. In GPA, this process commonly affects the upper respiratory tract, lungs, and glomeruli; granulomatous inflammation is particularly characteristic in the respiratory tract. That mechanism explains the clinically distinctive combination of destructive airway disease, pulmonary inflammation or haemorrhage, and rapidly progressive kidney injury. The patient may first appear to have recurrent sinus disease, but the pattern changes substantially when respiratory bleeding, hypoxaemia, or an active urinary sediment appears.