Can electrophysiology differentiate polyneuropathy with anti-MAG/SGPG antibodies from chronic inflammatory demyelinating polyneuropathy?

OBJECTIVES

Patients with polyneuropathy and antibodies to myelin-associated glycoprotein (MAG) and sulphated glucuronyl paragloboside (SGPG) differ from chronic inflammatory demyelinating polyneuropathy (CIDP) because of a slower, progressive course, symmetrical and predominantly sensory involvement of legs, predominantly distal slowing of motor conductions, and poorer response to therapy. We studied whether a wide set of electrophysiologic parameters may differentiate these two neuropathies.

METHODS

We reviewed the electrophysiological studies of 10 patients with anti-MAG/SGPG antibodies and 22 with CIDP examining: (1) motor conduction velocity and distal compound muscle action potential amplitude; (2) conduction block (CB) and temporal dispersion; (3) distal motor latency and terminal latency index (TLI); (4) F wave and proximal conduction time; and (5) sensory conduction and occurrence of abnormal median with normal sural sensory potential.

RESULTS

Anti-MAG/SGPG neuropathies showed: (1) more severe involvement of peroneal nerves; (2) more frequent disproportionate distal slowing of motor conductions (TLI< or =0.25) and absent sural potential, and (3) no CB. However 3/22 CIDP patients also had at least two nerves with TLI< or =0.25 and no CB.

CONCLUSIONS

Electrophysiologic findings suggest in anti-MAG/SGPG neuropathy a length-dependent process with a likely centripetal evolution. A disproportionate slowing of conduction in distal segments of motor nerves suggests the diagnosis of anti-MAG/SGPG neuropathy, although it is not pathognomonic.