Histology and ultrastructure of alterations in neuropathy

Histologic findings are described in nerves from men exposed to lead, from patients with discrete clinical signs of peripheral neuropathy, and from controls. Every nerve from control subjects showed an abnormality (paranodal remyelination, segmental remyelination, or regeneration) in teased fibers. The only histologic alteration in eight lead-exposed males without signs or symptoms of neuropathy was a slightly increased incidence of paranodal remyelination. Sixteen patients with discrete neurologic symptoms and signs had a loss of large myelinated fibers and an increased incidence of regenerated fibers among teased fibers. Electron microscopy of unmyelinated fibers showed an increased occurrence of Schwann-cell processes, of fibers undergoing degeneration, and of Schwann-cell subunits with many profiles as the earliest signs of abnormality. Clinically mild neuropathies may exhibit advanced regeneration in the case of unmyelinated fibers. The earliest sign of degeneration in myelinated fibers was a diminution in the number of axonal organelles.