Nerve conduction and excitability studies in peripheral nerve disorders.

PURPOSE OF REVIEW: The review is aimed at providing information about the role of nerve excitability studies in peripheral nerve disorders. It has been known for many years that the insight into peripheral nerve pathophysiology provided by conventional nerve conduction studies is limited. Nerve excitability studies are relatively novel but are acquiring an increasingly important role in the study of peripheral nerves. RECENT
FINDINGS: By measuring responses in nerve that are related to nodal function (strength-duration time constant, rheobase and recovery cycle) and internodal function (threshold electrotonus, current-threshold (I/V) relationship) it is possible to assess the function of transient and persistent Na+, fast and slow K+ and HCN inward rectifying channels as well as ion pumps. This has allowed insight into normal axon physiology and normal fluctuations of electrolyte concentrations. Studies of different metabolic neuropathies have assessed the influence of uremia, diabetes and ischemia, and the use of these methods in toxic neuropathies has allowed pinpointing damaging factors. Various mutations in ion channels associated with central nervous system disorders have been shown to have counterparts in the peripheral nervous system, in some instances without peripheral nervous system symptoms. Both hereditary and acquired demyelinating neuropathies have been studied and the effects on nerve pathophysiology have been compared with degeneration and regeneration of axons.
SUMMARY: Excitability testing holds promise for further understanding of peripheral nerve pathophysiology but is as yet not universally available. Interpretation may be challenging as changes in parameters may have different explanations, and modeling has been helpful in the use of the methods in clinical neurophysiology.