Motor unit number estimate of distal and proximal muscles in Charcot–Marie–Tooth disease

In order to determine the utility of motor unit number estimation (MUNE) in assessing axonal loss in chronic inherited neuropathies, we determined MUNEs in 54 patients with Charcot–Marie–Tooth (CMT) disease (29 patients with CMT‐1A, 13 with CMT‐X, and 12 with CMT‐2) by using spike‐triggered averaging (STA) of the ulnar‐innervated abductor digiti minimi/hypothenar muscles (ADM) and the musculo‐cutaneous innervated biceps/brachialis (BB) muscles. MUNEs were analyzed in relationship to the corresponding compound muscle action potential (CMAP) amplitudes as well as to clinical strength. Proximal muscles, which appeared strong clinically, had evidence of chronic denervation/reinnervation, although to a lesser extent than weak distal hand muscles, supporting the concept that axonal loss in CMT occurs in a length‐dependent fashion. The reduction in ADM‐MUNE strongly correlated with clinical weakness in the hand. Both the ADM‐MUNE and BB‐MUNE were abnormal more often than CMAP amplitude, probably reflecting extensive motor unit reconfiguration and enlargement that maintains CMAP amplitude despite severe motor unit loss. This study suggests that MUNE can assess motor unit loss in CMT and may better reflect axonal loss than CMAP amplitude. The STA technique of MUNE may be useful in longitudinal studies of proximal and distal motor unit changes in CMT. Muscle Nerve 28: 161–167, 2003

[1]  S. Hinderer,et al.  Neurological dysfunction and axonal degeneration in Charcot-Marie-Tooth disease type 1A. , 2000, Brain : a journal of neurology.

[2]  W. Brown,et al.  Methods for estimating numbers of motor units in biceps‐brachialis muscles and losses of motor units with aging , 1988, Muscle & nerve.

[3]  C. Bolton,et al.  Clinical and pathological observations in men lacking the gap junction protein connexin 32 , 2000, Muscle & nerve. Supplement.

[4]  J. Shefner,et al.  Reproducibility of motor unit number estimation in individual subjects , 2001, Muscle & nerve.

[5]  W. Brown,et al.  Genotype/Phenotype Correlations in X‐Linked Dominant Charcot‐Marie‐Tooth Disease , 1999, Annals of the New York Academy of Sciences.

[6]  M. Bromberg,et al.  Sources of error in the spike‐triggered averaging method of motor unit number estimation (MUNE) , 1995, Muscle & nerve.

[7]  P. Dyck,et al.  Longitudinal study of neuropathic deficits and nerve conduction abnormalities in hereditary motor and sensory neuropathy type 1 , 1989, Neurology.

[8]  Jeremy M. Shefner,et al.  Motor unit number estimation in human neurological diseases and animal models , 2001, Clinical Neurophysiology.

[9]  D Stashuk,et al.  EMG signal decomposition: how can it be accomplished and used? , 2001, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[10]  W. Brown,et al.  The estimated numbers and relative sizes of thenar motor units as selected by multiple point stimulation in young and older adults , 1993, Muscle & nerve.

[11]  G. Danieli,et al.  X-linked Charcot-Marie-Tooth disease , 2005, Human Genetics.

[12]  L. Gutmann,et al.  Longitudinal conduction studies in hereditary motor and sensory neuropathy type 1 , 1989, Muscle & nerve.

[13]  J. Engstrom,et al.  Statistical motor unit number estimation: Reproducibility and sources of error in patients with amyotrophic lateral sclerosis , 2000, Muscle & nerve.

[14]  T Doherty,et al.  Methods for Estimating the Numbers of Motor Units in Human Muscles , 1995, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.

[15]  Y. Agid,et al.  X-linked Charcot-Marie-Tooth disease with connexin 32 mutations , 1998, Neurology.

[16]  M. Bromberg.  Motor unit estimation: Reproducibility of the spike‐triggered averaging technique in normal and ALS subjects , 1993, Muscle & nerve.