Cryoimmunoglobulin IgGk with microtubular ultrastructure associated with pyoderma gangrenosum

Recurrent gangrenous leg ulcers were associated with a monoclonal IgGk cryoglobulinaemia, though without overt myeloma. Cryoprecipitation of the serum in vitro gave a reversible gel with microtubular structure, built from the monomer and with a high degree of order. The same structure was found distending the superficial vessels of the ulcer biopsy, as well as extravascularly. There was no vasculitis, and luminal obstruction appeared responsible for the ulceration. Microtubular structures occur in nature among diverse proteins and viruses. The protein studied here is similar to a reported instance of myeloma cryo-IgGk.