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The history of muscular dystrophy

University of British Columbia

The muscular dystrophies, Duchenne muscular dystrophy being the most common type, are a group for which there is no apparent pathology to the spinal motor neurons concomitant to progressive muscular degeneration. After this fact was established during the nineteenth century through postmortem examination, Charcot divided muscular disease into the "Great Classes" of myopathy and neuropathy. Erb's study of the histopathology brought a further division between the two before death and therefore the muscle biopsy became a tool for differential diagnosis. He also discovered that the response of muscle in myopathy and neuropathy to the application of electric current differed. While the response of myopathic muscle was progressively diminishing and equally so to the application of either galvanic or alternating current, neuropathic muscle maintained its ability to contract upon the application of galvanic current during the course of the disease. As well as the animating power of the nervous system by way of the anterior nerves, its trophic effect upon the muscle was evident by loss of volume upon interruption of its influence. Even though the absence of a lesion involving the spinal motor neurons or descending motor tracts was a constant in muscular dystrophy, there remained some reluctance to accept myopathy as being independent of the nervous system. According to the maintenance of the contractile response to galvanic current in neuropathy Erb suggested that there was a nerve centre other than that of the anterior cornua of the spinal cord which supplied the trophic influence. When he found histological features which were typical of myopathy in poliomyelitis he was convinced that muscular dystrophy was the result of a trophic disturbance. However, this theory was not sustainable because there was no anatomical evidence for a special trophic centre. In 1970 McComas again proposed that a neurogenic phenomenon was responsible for the pathogenesis of the muscular dystrophies. It was the re-emergence of a neurogenic hypothesis for muscular dystrophy which was the purpose of my exercise. In order to answer the question as to why a trophic theory reappeared I followed the research and theory regarding muscular dystrophy over time. The powerful effect of the somatic innervation upon muscle metabolism as determined by cross innervation experiments during the 1960's, set the stage for the reassertion of a trophic disturbance in muscular dystrophy. In addition, the division between myopathy and neuropathy had become less.distinct by 1970 in terms of histology, serum enzymes and the intramuscular innervation. Histological features considered to by typical of myopathy were seen in the biopsies of Charcot-Marie-Tooth disease and Kugelberg-Welander spinal muscular atrophy. As well, abnormally elevated serum levels of creatine phosphokinase which was characteristic of muscular dystrophy, were measured in these neuropathies. Changes in the intramuscular innervation of myotonic dystrophy and the animal model for muscular dystrophy also brought into question the myopathicity of muscular dystrophy. By 1970 the types of muscular dystrophy had been classified according to clinical and genetic criteria and were thus known to be genetically distinct diseases. A unifying hypothesis is always desireable and therefore, mental deficiency according to clinical assessment in Duchenne and myotonic dystrophy, the latter being an "impure" dystrophy, were considered to be supportive of the neurogenic hypothesis. "Hypertrophic paraplegia of infancy of cerebral origin" was the original title of what became known as Duchenne dystrophy. The frequent occurrence of mental retardation was the foundation of the name but with knowledge concerning the profound influence of the nerve upon the metabolism of the muscle, the alleged cerebral defect in Duchenne dystrophy favoured the neuropathicity of dystrophy even more.

Text

2010-08-16

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http://hdl.handle.net/2429/27477

Physiology

University of British Columbia

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