A 28-year-old man complains of nasal obstruction, bloody nose, cough, and bloody sputum. A chest X-ray displays cavitated lesions and multiple nodules within both lung fields. Urinalysis reveals 3+ hematuria and red blood cell casts. Laboratory studies show anemia and elevated serum levels of C-ANCA (antineutrophil cytoplasmic antibody). Peripheral eosinophils are not increased. A renal biopsy exhibits focal glomerular necrosis with crescents and vasculitis affecting arterioles and venules. Which of the following best describes the renal disease of the patient?

Focal necrotizing glomerulonephritis is one of the early features of Wegener granulomatosis. The pathogenesis of this renal disease is not known, but it is thought to be immune mediated because most patients have antibodies to neutrophils (ANCA). These autoantibodies activate neutrophils and cause them to adhere to endothelial cells, release toxic oxygen metabolites, degranulate, and kill the endothelial cells. Exudation of inflammatory cells through the disrupted, segmentally necrotic basement membrane leads to the formation of crescents. Clinically, the disease presents as RPGN, a clinical term that is used to denote the rapid onset of renal failure caused by severe glomerular injury. Wegener granulomatosis does not cause membranoproliferative glomerulonephritis (choices D and E).Diagnosis: Wegener granulomatosis, crescentic glomerulonephritis