Esnaultet al studied serum from 125 patients with MM with IF and radioimmunoassay and found7 with positive IgG-ANCA and 5 with positive IgM-ANCA.5,7,9,15 Given the differing treatmentsbetween MM and systemic vasculitis, a renal biopsy was necessary for definitivediagnosis. Here, CD40LG is linked to necrotizing vasculitis.