Correlation between denervation activity and compound muscle action potential amplitude in hereditary motor and sensory neuropathy I and II.

Studying the electrophysiological characteristics of the various types of Charcot-Marie-Tooth disease is important in the understanding of its pathophysiology. The purpose of this study was to identify the frequency of fibrillation potentials and positive sharp waves (FP/PWs) in HMSN I and II and, since they are indices of denervation, to elucidate whether they are correlated with the amplitude of compound muscle action potentials (CMAP). We reviewed the electrophysiological findings of 47 patients who have been studied in our hospital and found to suffer from Charcot-Marie-Tooth polyneuropathy. FP/PW were graded according to a 4-grade scale and the 38 m/sec criterion for motor conduction velocity (MCV) was used for distinction between HMSN I and II subgroups. Seventy percent of HMSN II patients and 81% of HMSN I patients showed fibrillation potentials in the upper or lower limbs. There was no difference in the frequency of FP/PW appearance between the two groups. In the HMSN II group the FP/PW grade correlated with CMAP amplitude in the upper limbs. In both groups there was no correlation between FP/PW grade and MCV. Our findings might indicate that in HMSN I there is a considerable axonal destruction that occurs concurrently with myelin loss.