Focal myelin swellings and tomacula in anti-MAG IgM paraproteinaemic neuropathy: Novel teased nerve fiber studies

Focal myelin swellings and tomacula in teased nerve fibers from a case of I gM anti-myelin-associated glycoprotein (MAG) paraproteinaemic neuropathy we re examined using a novel technique. Five different morphologic abnormaliti es were identified-myelin sheath outfolding, myelin sheath infolding, enlar gement of the adaxonal space, myelin degeneration, multiple increased conce ntric loops-and a combination of these structural abnormalities often occur in association with myelin degeneration. Similar structural changes were f ound in externally normal segments of teased fibers without evidence of mye lin swelling or tomacula from the same case. These structural abnormalities are consistent with a disturbance of the normal adhesion functions of MAG in the maintenance of axon-myelin relationships.