IgM cryoglobulin deposits in the peripheral nerve.

In a patient with Waldenström's macroglobulinaemia and peripheral neuropathy, direct immunofluorescence of a peripheral nerve revealed the presence of abundant IgM and kappa light chain deposits in the endoneurium. Electron microscopic examination showed the microtubular structure of these endoneurial deposits, which strongly suggested the presence of cryoglobulin; this was then found in the serum.