[Fatal peripheral neuropathy with predominant motor involvement associated with anti-MAG IgM monoclonal gammapathy].

A 75 year old woman died of predominantly motor peripheral neuropathy with amyotrophy and fasciculations progressing to tetraplegia and death within 19 months. There was a mild distal sensory loss. At electrophysiology, the pattern was initially demyelinating and later became axonal. Nerve biopsy disclosed severe myelinated and unmyelinated fiber loss with wallerian degeneration. The remaining fibers had demyelination widening of the external myelin lamellae and intense hypermyelination. Serum contained an anti-MAG monoclonal IgM reacting with SGPG. Two siblings without monoclonal gammopathy had died of definite amyotrophic lateral sclerosis. This family association is discussed.