Direct immunofluorescence findings in peripheral nerve from patients with diabetic neuropathy.

Direct immunofluorescence examination was performed on peripheral nerve from 16 patients with diabetes mellitus and 53 additional patients with peripheral neuropathy of diverse cause. Six nerves from patients with diabetes mellitus yielded positive findings: 4 had granular and lamellar deposition of IgM within the perineurium (of which 2 also had fibrinogen, IgA, C3, and albumin and 1 also had IgG); 1 had IgM, C3, and C4, and perineurial fibrinogen; the sixth contained linear perineurial C3 and fibrinogen. These 6 nerves contained axonal degeneration (3), axonal degeneration with chronic demyelination (1), microvasculitis with wallerian degeneration (1), and no pathological change (1). Sixteen of 53 nerves from nondiabetics yielded positive findings with immunofluorescence, possibly as a result of vascular leakage or as a manifestation of impaired removal of plasma proteins. The deposition of immunoreactants, as well as other plasma proteins, in peripheral nerve from patients with diabetes mellitus probably represents a "trapping" phenomenon reflecting altered basement membrane permeability. Alternatively, the changes could reflect a defect in the blood-nerve barrier in diabetic microangiopathy.