Features of cryocrystalglobulinemia. (A) Painful vasculitis produced by an IgGκ cryocrystalglobulin. Plasmapheresis rapidly resolved the vasculitis, and subsequent treatment with high-dose dexamethasone significantly reduced (by 70%) the concentration of the monoclonal IgGκ, leading to complete clinical remission. (B) Crystals formed after storing the serum at 4°C for 24 hours. Image was visualized using a Nikon Eclipse E600 microscope equipped with a Nikon Pan Fluor 20 ×/0.50 NA objective with no staining. Image was acquired using a Leica DFC 480 camera and Leica IM50 Image Manager software.