[Electrodiagnostic features in inflammatory demyelinating polyneuropathy].

Abstract

Demyelinating conduction block is an important hallmark to distinguish chronic inflammatory demyelinating polyneuropathy (CIDP) from hereditary neuropathies, motor neuron disease and other axonal type neuropathies. The electrodiagnostic criteria of partial conduction block proposed by Asbury and Cornblath, more than 20% drop in CMAP amplitude between proximal and distal sites (e.g. elbow and wrist), may be inadequate, because 20% to 30% drop sometimes occurs in cases with hereditary demyelinating neuropathies. Rhee et al showed that pure temporal dispersion can produce amplitude reduction up to 50% without conduction block. This reduction between elbow and wrist is equivalent to 2% drop/cm. Since lesions are multifocal in CIDP, more than 2% drop/cm in relatively short segments could be a convincing finding of conduction block of CIDP or multifocal motor neuropathy. Our inching study has revealed that chance of lesion is equal from distal to proximal along the nerves of CIDP. However, it is not true in AIDP; most distal sites, roots, and physiological entrapment sites are more fragile, and early demyelination and secondary axonal degeneration start there. Axonal degeneration easily makes demyelinating conduction changes; therefore, in diagnosis of axonal form of AIDP, the possibility of early Wallerian degeneration has to be ruled out by careful follow-up, and delayed F-wave or long-latency units definitely go against the primary axonal pathology.