Electrodiagnostic criteria for Guillain-Barrè syndrome: a critical revision and the need for an update.

Electrophysiology plays a determinant role in Guillain-Barré syndrome (GBS) diagnosis, classification of the subtypes and in establishing prognosis. In the last three decades, different electrodiagnostic criteria sets have been proposed for acute inflammatory demyelinating neuropathy (AIDP), acute motor axonal neuropathy (AMAN) and acute motor and sensory axonal neuropathy (AMSAN). Criteria sets for AIDP varied for the parameters indicative of demyelination considered, for the cut-off limits and the number of required abnormalities (all a priori established) showing different sensitivities. Criteria sets for AMAN and AMSAN were proposed on the initial assumption that these subtypes were pathologically characterised by simple axonal degeneration. However, some AMAN patients show transient conduction block/slowing in intermediate and distal nerve segments, mimicking demyelination but without the development of abnormal temporal dispersion, named reversible conduction failure (RCF). The lack of distinction between RCF and demyelinating conduction block leads to fallaciously classify AMAN patients with RCF as AIDP or AMAN with axonal degeneration. Serial electrophysiological studies are mandatory for proper diagnosis of GBS subtypes, identification of pathophysiological mechanisms and prognosis. More reliable electrodiagnostic criteria should be devised to distinguish axonal and demyelinating subtypes of GBS, taking into consideration the RCF pattern and focussing on temporal dispersion.