S87 Issues in the electrodiagnosis of Guillain-Barré syndrome subtypes

Abstract

Electrophysiology plays a determinant role in Guillain–Barre syndrome (GBS) diagnosis, classification of the subtypes and in establishing prognosis. Acute inflammatory demyelinating polyradiculoneuropathy (AIDP) has been electrophysiologically characterized by conduction slowing, conduction block, and temporal dispersion. Acute motor axonal neuropathy (AMAN) was initially thought to be characterized by simple axonal degeneration and the electrophysiological correlate limited to reduced amplitude of compound muscle action potentials. However AMAN and acute motor and sensory axonal neuropathy (AMSAN) patients show transient conduction block/slowing due to nodal dysfunction mimicking demyelination but without the development of abnormal temporal dispersion. This has been referred to as reversible conduction failure (RCF) and it is thought to be due to the attack of antiganglioside antibodies at the Ranvier node inducing a transitory dysfunction not progressing to axonal degeneration both in motor and sensory fibers. RCF it can be recognized only by serial studies and it is not included in the current electrodiagnostic criteria of GBS. The lack of distinction between RCF and demyelinating conduction block led to erroneous classification in up to 38% of patients. There is a need for an innovative approach to reach an earlier and more accurate electrodiagnosis based on a single study. In this talk the pitfalls in GBS electrodiagnosis will be highlighted and the inadequacy of current criteria discussed. A new criteria set for AIDP, AMAN and AMSAN, defining also the cut-offs for RCF in motor and sensory fibers, will be illustrated and the electrodiagnostic accuracy of a statistical method of supervised classification (sparse linear discriminant analysis) reported.