Immunoelectron identification of endoneurial IgM deposits in four patients with Waldenström's macroglobulinemia: a specific ultrastructural pattern related to the presence of cryoglobulin in one case.

In four patients with Waldenstrom's macroglobulinemia and peripheral neuropathy, direct immunofluorescence on a peripheral nerve biopsy revealed the presence of IgM deposits in the endoneurium. At ultrastructural examination, these endoneurial deposits were granulo-fibrillar in three cases, and tubular in the fourth, in whom a cryoglobulin was evidenced in the serum. In each case the endoneurial deposits were also identified as IgM by post-embedding immunoelectron microscopy with good preservation of the characteristic ultrastructural details