• Guillain-Barre Syndrome
• Ganglioside

Electrophysiology plays an important role in Guillain–Barré syndrome (GBS) diagnosis, classification in subtypes and in establishing prognosis. Different criteria sets have been proposed for electrodiagnosis of 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 considered indicative of demyelination, for the cut-offs and the number of required abnormalities, showing different sensitivity and specificity.1–3 Criteria sets for axonal GBS (AMAN and AMSAN) were proposed on the initial assumption that these subtypes were pathologically characterised by simple axonal degeneration.1 ,2 However, some AMAN and AMSAN 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).4–6 Evidence from animal models and clinical studies indicate that RCF is due to the attack of antiganglioside antibodies at the Ranvier node inducing a transitory dysfunction/disruption not progressing to axonal degeneration.7 ,8 The lack of distinction between RCF and demyelinating conduction block leads to fallaciously classify AMAN patients with RCF as AIDP or, in presence of reduced distal compound muscle action potentials (CMAP), as AMAN with axonal degeneration and erroneously formulate a poor prognosis. RCF is an a posteriori diagnosis which can be made only by serial recordings, and it is not included in the commonly employed criteria.1 ,2 ,9 ,10

Rajabally and coworkers hypothesised that using higher cut-offs for demyelination (based on criteria proposed by Van den Bergh and Pieret),3 and considering a proximal/distal CMAP amplitude ratio <0.7 in 2 nerves (without other features of demyelination) as indicative of RCF, might suffice a single study for electrodiagnosis of GBS subtypes.11 They retrospectively examined 365 patients and, applying the Hadden's critera at …