Axonal GBS is pathophysiologically characterised not only by axonal degeneration but also by reversible conduction failure at the axolemma of the Ranvier node. The lack of distinction among demyelinating conduction block, reversible conduction failure and length-dependent compound muscle action potential amplitude reduction may fallaciously classify patients with axonal GBS as having AIDP. Serial electrophysiological studies are mandatory for proper diagnosis of GBS subtypes and the identification of pathophysiological mechanisms of muscle weakness. More reliable electrodiagnostic criteria taking into consideration the reversible conduction failure pattern should be devised.

To define numerically the clinical severity of facioscapulohumeral muscular dystrophy (FSHD), we developed a protocol that quantifies muscle weakness by combining the functional evaluation of six muscle groups affected in this disease. To validate reproducibility of the protocol, 69 patients were recruited. Each patient was evaluated by at least five neurologists, and an FSHD severity score was given by each examiner. The degree of agreement among clinicians' evaluations was measured by kappa-statistics. Nineteen subjects received a score between 0 and 1, 9 had a score between 2 and 4, 20 received a score between 5 and 10, and 8 had a score between 11 and 15. Of the 13 subjects with D4Z4 alleles within the normal range (ranging from 10 to 150 repeats), 12 obtained a score of 0 and only 1 had a score of 1. Kappa-statistics showed a very high concordance for all muscle groups. We developed a simple, reliable, easily used tool to define the clinical expression of FSHD. Longitudinal studies will assess its sensitivity and utility in measuring changes for widespread use.

Sensory fibres are often involved subclinically in AMAN. Reversible conduction failure may develop in sensory as well as motor fibres in both AMAN and AMSAN. AMAN and AMSAN represent a continuum in axonal GBS.

In two patients with the pharyngeal-cervical-brachial variant (PCB) of Guillain-Barré syndrome (GBS), low amplitude distal compound muscle action potentials and partial motor conduction blocks normalized without development of excessive temporal dispersion within 4 weeks. Sensory nerve action potentials significantly improved in amplitude or, when absent, rapidly became recordable at follow-up. Besides axonal degeneration, PCB is characterized by reversible conduction failure in both motor and sensory fibers and is in the continuous spectrum of axonal GBS subtypes.

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