Clinico-electrophysiological correlation of extensor digitorum brevis muscle atrophy in children with charcot-marie-tooth disease 1A duplication.

The purpose of the study is to describe the electrophysiologic abnormalities accounting for the appearance and progression of extensor digitorum brevis (EDB) muscle atrophy in Charcot-Marie-Tooth-disease type 1A (CMT-1A) children. Twelve children with CMT-1A duplication were serially evaluated. Initial ages of clinico-electrophysiological exams ranged from 1 month to 4 years (mean: 2 years) and final ages from 6 to 23 years (mean: 13). All subjects had two or more electrophysiological studies of the peroneal nerve. EDB atrophy was observed in two out of 12 (17%) patients by the age of 5, in eight out of ten (80%) examined between 5 and 9 years, and in all eight (100%) patients who had reached the second decade at the end. Nerve conduction maturation was systematically abnormal, but by age of 5 the mean values of nerve conduction parameters of peroneal nerve did not significantly differ from those in older patients. Compound muscle action potential (CMAP) amplitudes of EDB were reduced in 42% of cases initially and 100% upon last exam. Furthermore, a constant finding throughout the study was progressive attenuation of CMAPs, these becoming unobtainable in four cases. EDB muscle atrophy in CMT-1A children is an age-dependent sign which is accounted for by gradual reduction of the distal peroneal nerve CMAP amplitudes.