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The muscular dystrophies are a group of progressive hereditary degenerative diseases of skeletal muscles. The innervation of the affected muscles, in contrast to that of the neuropathic and spinal atrophies, is unaffected. In the last several decades, their purely muscular nature has been definitively demonstrated by the finding of genetic defects that involve proteins expressed exclusively in muscle. The intensity of the degenerative changes in muscle and the cellular response and intensity of the regenerative changes distinguish the dystrophies histologically from other diseases of muscle and also have implications regarding their pathogenesis. The category of more benign and relatively nonprogressive myopathies—each named from its special histopathologic appearance, such as central core, nemaline, mitochondrial, and centronuclear diseases—present greater difficulty in classification. Like the dystrophies, they are primarily diseases of muscle and are heredofamilial in nature, but they are placed in a separate category because of a nonprogressive or slowly progressive course and their distinctive histochemical and ultrastructural features, as discussed in Chap. 52.

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The current clinical classification of the muscular dystrophies is based mainly on the distribution of the dominant muscle weakness, however, several of the classical types have retained their eponymic designations: Duchenne, Becker, Emery-Dreifuss, Landouzy-Dejerine, Miyoshi, Welander, Fazio-Londe, and Bethlem are among the ones that still have utility in shorthand. To these are added myotonic dystrophy and a group of so-called congenital muscular dystrophies, usually severe in degree.

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The extraordinary depth of information regarding the molecular nature of the dystrophies is one of the most gratifying developments of modern neuroscience. The majority of the dystrophies are caused by changes in structural elements of the muscle cell, mainly in its membrane, but other important mechanisms also are being identified, such as altered messenger RNA. In keeping with the outlook expressed throughout the book, we adhere to a clinical orientation in describing the muscular dystrophies but make clear that treatment in the future will be determined based on understanding of molecular mechanisms. Each of the muscular dystrophies is described in accordance with this scheme.

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Historical Background

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The differentiation of dystrophic diseases of muscle from those secondary to neuronal degeneration was an achievement of neurologists of the second half of the nineteenth century. Isolated cases of muscular dystrophy had been described earlier, but no distinction was made between neuropathic and myopathic disease. In 1855, the French neurologist Duchenne described the progressive muscular atrophy of childhood that now bears his name. However, it was not until the second edition of his monograph in 1861 that the “hypertrophic paraplegia of infancy” was recognized as a distinct syndrome. By 1868 he was able to write a comprehensive description of 13 cases and recognized that the disease was muscular in origin and restricted to males. Gowers in 1879 gave a masterful account of 21 personally observed cases and called attention to the characteristic way in which such patients arose from the floor (Gowers sign). Erb, in 1891, crystallized the ...

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