Vasculitic neuropathy in a patient with cryoglobulinemia and anti-MAG IGM monoclonal gammopathy.

A patient with sensorimotor mononeuritis multiplex had a type II cryoglobulin with an IgM kappa M-protein that appeared to contain monoclonal anti-MAG antibodies of the same isotype. A sural nerve biopsy demonstrated necrotizing arteritis and features of both axonal degeneration and demyelination. IgM kappa and C3 deposits were present on the myelin sheath of some residual nerve fibers. The findings suggest that the anti-MAG antibodies contributed to the myelin damage, while cryoprecipitates may have caused the vasculitis and axonal degeneration.