- Section of the kidney with cortex and medulla.
- Fibrinoid necrosis of medium and small-sized muscular arteries (arcuate, interlobular arteries). The arterial wall appears thickened and homogenously eosinophilic. Neutrophils, eosinophils and histiocytes may be detected in the wall. In some instances a predominant mononuclear infiltrate is seen.
- Arterial walls are often not uniformly affected. Partial thickening of the arterial wall renders a nodular aspect (thus the name: ‘nodosa’).
- Renal parenchyma with hemorrhage and necrosis.
Usually, constitutional signs and symptoms of inflammation are present (fever, malaise, anorexia, myalgias and arthralgias). The manifestations of tissue injury are very variable (skin ulcerations, painful subcutaneous nodules, peripheral neuropathy, pericarditis, myocardial infarction, abdominal pain or bleeding). Renal involvement is frequent, occurring in more than 50% of patients. Presenting signs may be hematuria, mild proteinuria, renal insufficiency and hypertension.