Sensitivity of conventional motor nerve conduction examination in detecting patchy demyelination: A simulated model Pietro Caliandro a,b, * , Erik Sta ˚lberg c , Giuseppe La Torre d , Luca Padua a,b a Institute of Neurology, Universita ` Cattolica, Roma, Italy b Fondazione Pro Iuventute Don Carlo Gnocchi, Roma, Italy c Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden d Epidemiology and Biostatistics Unit, Institute of Hygiene, Universita ` Cattolica, Roma, Italy Accepted 17 April 2007 Abstract Objective: To evaluate, in 5 simulated motor nerves with patchy demyelination: (1) the sensitivity of the conventional motor conduction examination; (2) the conduction velocity of single axons (SA-CV). Methods: Four damaged segments were simulated in each nerve. Myelin impairment was generated by varying two parameters: (1) per- cent reduction in conduction velocity, i.e. degree of damage (DEGREE); (2) percentage of affected axons, i.e. extent of damage (EXTENT). Myelin impairment was simulated in axons with different diameters. We evaluated: (1) conduction velocity; (2) temporal dispersion of the negative phase of compound motor action potential (CMAP); (3) amplitude decay of CMAP; (4) SA-CV of 20 ran- domly-chosen axons. Results: When the damage involved both large and small axons, the conduction velocity was pathological only when severe myelin dam- age involved a large number of axons. Temporal dispersion and amplitude decay were more sensitive than conduction velocity in detect- ing the damage. In damage involving only large axons or only small axons, all parameters remained in the normal range. SA-CV evaluation was much more sensitive than the conventional studies, regardless of the diameter of the damaged axons. Conclusions: Conventional studies are not sensitive in detecting minimal myelin damage. Decomposing the CMAPs and randomly study- ing 20 SA-CVs would increase the sensitivity of damage detection. Significance: These results contribute to a better understanding of the relationship between axonal properties and neurophysiological findings in motor nerve demyelination. Ó 2007 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Demyelination; Myelinopathy; Conduction velocity; Neurography 1. Introduction The compound motor action potential (CMAP), which is recorded with surface electrodes, represents the sum of the activity generated by motor units within a muscle after nerve stimulation. The size and shape of the CMAP are determined by the recording electrode, the shape characteristics of individual motor unit action potentials, the position of the motor unit in the muscle, the number of motor units, the distance that the impulse must cover along the nerve, and the range and distribu- tion of conduction velocities in the alpha motor fibres (Gasser and Erlanger, 1927; Cummins et al., 1979; Tho- mas et al., 1959; Kakuda et al., 1992; Feinstein et al., 1955; Olney et al., 1987). The conduction velocity of each normal axon depends on the external nerve fibre diameter (Gasser and Grundfest, 1939; Hursh, 1939; McLeod and Wray, 1967; Waxman and Bennett, 1972; Ritchie, 1982), as well as membrane characteristics, tem- perature, and the properties of the myelin sheath (De Jesus et al., 1973; Todnem et al., 1989; Dioszeghy and Sta ˚lberg, 1992). 1388-2457/$32.00 Ó 2007 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2007.04.011 * Corresponding author. Address: Institute of Neurology, Largo F. Vito 1, 00168 Roma, Italy. Tel.: +39 06 30154435; fax: +39 06 35501909. E-mail address: p.caliandro@rm.unicatt.it (P. Caliandro). www.elsevier.com/locate/clinph Clinical Neurophysiology 118 (2007) 1577–1585