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Disorder of muscle contraction processes in sex-linked (Duchenne) muscular dystrophy, with correlative electromyographic study of myopathic involvement in small hand muscles

par Desmedt, Jean Edouard ;Emeryk, Barbara;Renoirte, P.;Hainaut, Karl
Référence The American journal of medicine, 45, 6, page (853-872)
Publication Publié, 1968-12

Article révisé par les pairs

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Résumé :

The aim of this investigation is to develop the pathophysiologic analysis of the contractile disorder in muscular dystrophy. The adductor pollicis muscle was investigated by needle electromyography and by nerve stimulation methods in six normal boys serving as controls, and in seventeen hands of fifteen patients with Duchenne muscular dystrophy. Being involved later than proximal muscles by the disease, the small hand muscles allowed us to study a whole spectrum of changes, from the preclinical stage to advanced myogenic atrophy. The anomalies of the voluntary motor unit potentials disclosed by needle electromyography bear a unique relation to the disturbances of contractile processes in the same muscle. These combined features consistently reflect the peculiar dynamics of disease in the hand muscles but they cannot be predicted in any given patient from the over-all clinical data (age, gait disturbances, level of enzymes creatine phosphokinase and lactic dehydrogenase in blood, etc.).In the course of Duchenne dystrophy the disorder of contraction in the adductor pollicis muscle antedates any recordable anomaly in the electrical activity of the same muscle. Several changes indicate that the capability for tension development is decreased with respect to that of the muscle of normal boys of similar age: reduction of tetanic force (Po), of twitch force (Pt) and of the maximum rate of tension development in tetanus (Ro) and in twitch (Rt). Consistent changes are recorded in the staircase profiles of the isometric twitch during two per second stimulation of the motor nerve. They point to an anomaly in the process of activation of the myofilaments. The contraction kinetics are not grossly damaged by Duchenne dystrophy. The contraction time (CT) of the twitch does not appear to change significantly, which suggests that the myosin of the still excitable dystrophic muscle fibers has a normal ATPase activity. The maximum speed of relaxation per kg., St:Pt, is reduced from 10 to 6.5 in the patients. The relaxation time (T1/2R) is increased by +23 per cent. However, both the relaxation time and speed change to approximate normal values during two per second stimulation. The paper provides a quantitative reference base for correlative biochemical, pathophysiologic and electron microscopic studies of the still unknown etiology of this disorder.