Distal accentuation of conduction slowing in polyneuropathy associated with antibodies to myelin-associated glycoprotein and sulphated glucuronyl paragloboside

Abstract

In four patients with a chronic, demyelinating polyneuropathy associated with monoclonal IgM antibodies to myelin-associated glycoprotein (MAG) and sulphated glucuronyl paragloboside (SGPG), we have observed a marked prolongation of distal motor latencies disproportionate to proximal segment-conduction velocities, in nearly all nerves studied. Distal accentuation of conduction slowing distinguished these patients from those with Charcot-Marie-Tooth polyneuropathy type 1A, chronic inflammatory polyneuropathy, and from controls, as demonstrated by regression of distal motor latency on proximal conduction velocity. Sixteen of 21 nerves (76%) studied in the patients with anti-MAG/SGPG polyneuropathy had a terminal latency index of < or = 0.25 versus 11 of 195 nerves (6%) of Charcot-Marie-Tooth polyneuropathy type 1A patients, three of 49 nerves (6%) of patients with chronic inflammatory polyneuropathy and none of the controls (P = 0.0001). Recognition of this unique pattern of generalized, distally predominant conduction slowing in anti-MAG/SGPG polyneuropathy may be useful in clinically distinguishing this from other chronic demyelinating polyneuropathies, and in possibly providing insights into the pathophysiology of this disorder.