Macro-EMG and muscle biopsy of paretic foot dorsiflexors in Charcot–Marie–Tooth disease

Twelve patients with Charcot–Marie–Tooth disease type 1 (CMT1) and 11 with type 2 (CMT2), with a clinically similar range of muscle weakness of foot dorsiflexion, were subjected to macroelectromyographic (macro-EMG) examination and muscle biopsy of the tibialis anterior (TA) muscle in order to elucidate the denervation–reinnervation process in the two CMT forms. The macro-EMG examination showed higher median amplitude values and median area values for the CMT1 patients, with a mean value of 1515 ± 1222 μV and 3953 ± 2613 μV · ms, respectively, than for the CMT2 patients, with a mean value of 865 ± 971 μV and 2525 ± 2575 μV · ms, respectively. When corrected for muscle fiber area, the difference was statistically significant for amplitude (P < 0.01) and area (P < 0.05). For CMT1 patients, the increase of macro-EMG potentials varied from 2 to 14 times and for CMT2 patients from less than 1 to 8 times larger than corresponding age-matched values. Muscle biopsies of TA showed that the type I fiber percentage was significantly higher (P < 0.05) in the CMT1 patients (99 ± 2.2%) than in the CMT2 patients (86 ± 12.3%). Morphometric data showed a significantly higher (P < 0.05) mean type I fiber area in the CMT2 patients (8130 ± 4721 μm²) when compared with the CMT1 patients (5066 ± 3431 μm²). The present data indicate that denervation in CMT1 is associated with prominent collateral reinnervation but only minor muscle fiber changes, whereas in CMT2 there is only minor collateral reinnervation but prominent muscle fiber changes including significant muscle fiber hypertrophy. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 217–222, 2000.