Conference lecture: Electrophysiological diagnosis of inflammatory demyelinating neuropathies

Electrophysiology plays a crucial role in the characterization and diagnosis of peripheral neuropathies. It provides insight in the type and mechanism of peripheral neuropathy by giving information on the spatial pattern, the fibre type involved, pathology (axonal, demyelinating), and the severity and time course. Inflammatory demyelinating neuropathies constitute a significant proportion of the acquired peripheral neuropathies. They include Guillain-Barre syndrome (GBS), chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), multifocal motor neuropathy (MMN), multifocal demyelinating neuropathy with persistent conduction block (Lewis-Sumner syndrome), and paraproteinemic neuropathies. A proper diagnosis as early as possible is very important because timely immune treatment can largely reduce morbidity and disability. The diagnosis is based on a constellation of clinical and laboratory features, including electrophysiological studies, spinal fluid examination, and in selected cases serological studies and peripheral nerve biopsy. Electrophysiological studies are key in the early detection and characterization of inflammatory demyelinating neuropathies and in differentiating these from primary axonal neuropathies. In CIDP, electrophysiological criteria for demyelination are designed to exclude abnormalities that can be explained by axonal degeneration (Eur J Neurol 2010). Therefore, lesser degrees of demyelination cannot be defined with certainty. Optimised electrophysiological criteria are capable, however, to support the diagnosis with different levels of probability (possible, probable, definite) in the very large majority of cases. In GBS, much effort has gone into developing criteria which can distinguish axonal and demyelinating subtypes. The discovery of reversible conduction failure (RCF) has led to the concept of nodopathy/paranodopathy, where conduction slowing and conduction block are due to the immune attack mainly at the nodal axolemma level. There is no actual demyelinisation as defined pathologically and if the immune attack continues, conduction failure may not reverse and axonal degeneration will ensue. Recent electrophysiological studies support this pathophysiological mechanism and show that the dichotomous distinction between axonal and demyelinating in GBS is not tenable (Muscle nerve, 2018).