Electrodiagnosis of polyneuropathy

Electrodiagnostic studies comprising electromyography (EMG) and nerve condu ction studies (NCS) are well-established objective methods for the diagnosi s, quantification and classification of polyneuropathies (PNP). This paper reviews examination techniques, their pathophysiological interpretation, ex amination strategies and diagnostic criteria for the diagnosis and classifi cation of a PNP. The routine electrodiagnostic evaluation includes sensory NCSs performed with surface or needle electrodes, motor NCSs, F-wave studie s and EMG by qualitative or quantitative techniques. Sensory NCSs and F-wav e studies have a high sensitivity in PNPs and the different techniques comp lement each other. The distinction between a PNP with predominantly axonal loss and a PNP with predominantly demyelination is one of the major aims of the electrophysiological examination. There are, however, large variation in suggested criteria for predominantly demyelination. The degree of slowin g in conduction taken to indicate demyelination varies between a decrease o f 50 to 30% from mean of controls, distal latency prolongation criteria var y from 35% to 70% of mean of controls, F-wave latency prolongation criteria vary from 120% to 150% of upper limit of controls, and criteria for partia l motor conduction block vary from 11 to 50% reduction of CMAP amplitude an d/or area between proximal and distal stimulation. Needle EMG studies may b e valuable in order to detect and quantify denervation activity, to assess chronicity by an evaluation of the extent of reinnervation, and to evaluate the topographical distribution of changes. It is concluded that electrodia gnostic studies are valuable in patients with suspected PNP and the results may have consequences for prognosis and therapy of individual patients. La rge variation in examination techniques, strategies, interpretations and di agnostic criteria have been found among electromyographers and it is sugges ted that the value of electrodiagnostic studies may be further improved by international standardisation. (C) 2000 Editions scientifiques et medicales Elsevier SAS.