[Value of electrophysiology in the follow-up of dysimmune polyneuropathies]

Electrophysiological follow-up of dysimmune neuropathies leads to consider various situations depending on the type of neuropathy. In Guillain-Barré syndrome, studies have highlighted the usefulness of early measurements of distal motor latencies and late responses at onset of paralysis, and of motor conduction velocities (MCVs), conduction blocks, sensory nerve action potentials and possible signs of axonal degeneration at the plateau of symptoms. However, none of these signs are predictive of clinical recovery, except early appearance of axonal degeneration which often indicates poor prognosis. In chronic inflammatory idiopathic demyelinating polyneuropathies, the follow-up mostly relies on motor conduction studies: increase or slowing of MCVs, shortening or prolongation of distal motor latencies, improvement or lengthening/disappearance of late responses and, more ancillary, sensory nerve action potential changes. Signs of axonal degeneration can worsen the prognosis. In multiple motor neuropathies with persistent conduction blocks, the most relevant electrophysiological criterion is increase or reduction of conduction blocks, as well as occurrence of new blocks and signs of axonal degeneration. In neuropathies associated with IgM monoclonal gammopathy of undetermined significance (MGUS) with anti-MAG antibodies, the electrophysiological follow-up mostly relies on the comparison between MCVs and distal motor latencies, as well as improvement or worsening of sensory nerve action potential amplitudes, and possible signs of axonal degeneration. In all those neuropathies however, therapeutic choices remain largely dependent on clinical scores, which have become increasingly standardized in recent years, although scales used by different groups are not universally accepted.