LAUSR

An 84-year-old woman presented with a 2-month history of multiple finger arthritis, peripheral neuropathy, and retiform purpura on the abdomen and extremities (Fig. 1a). Laboratory test results showed renal function impairment with hematuria and proteinuria, elevated serum levels of C-reactive protein and rheumatoid factor (RF) and C4 hypocomplementemia. The patient had no history of kidney disease, hepatitis, recent infections, recent catheterization, or anticoagulant administration. An IgM monoclonal component was found on serum protein electrophoresis. Cryoglobulins were not detected. Autoimmune blood tests, including antinuclear antibodies, antineutrophil cytoplasmic antibodies, anticardiolipin antibodies, and lupus anticoagulant, were negative. Hepatitis C, B, and human immunodeficiency virus serologic studies were also negative. A CT scan did not show any vascular abnormalities of the renal arteries. A skin biopsy was conducted (Fig. 1b,c).