Neurogenic muscle disorders

The clinical and histopathological features of individual neurogenic muscle disorders are determined to a large extent by the balance of the opposing processes of denervation and reinnervation, at least as far as the muscle dysfunction is concerned. The involvement of upper motor neurons in some of these disorders is outside the scope of this chapter and will only be referred to in passing. 

To cover these various disorders in an orderly and comprehensive manner, the following sections are devoted, respectively, to the muscular dystrophies the congenital myopathies the metabolic myopathies the myotonias, periodic paralyses, and malignant hyperpyrexia the neurogenic disorders the inflammatory muscle disorders the endocrine myopathies and the drug-induced and toxic myopathies. 

Diseases affecting skeletal muscle are not always primary diseases of muscle, and it is necessary first to determine whether a particular disorder is a primary disease of muscle, is neurogenic in origin, is an inflammatory disorder, or results from vascular insufficiency. A primary disease of muscle is one in which the skeletal muscle fibers are the primary target of the disease. Neurogenic disorders are those in which weakness, atrophy, or abnormal activity arises as a result of pathological processes in the peripheral or central nervous system. Inflammatory disorders may result in T-cell mediated muscle damage and are often associated with viral infections. Vascular insufficiency as a result of occlusion in any part of the muscle vasculature can cause severe disorders of muscle, especially in terms of pain, metabolic insufficiency, and weakness. 

Primary myopathies fall into a number of discrete groups the inherited diseases of muscle, the metabolic myopathies, the neurogenic disorders, and the acquired disorders of muscle. 

Q2 Constipation is a condition in which faecal material moves too slowly through the large intestine. As a result too much water is reabsorbed hard, dry faeces which are difficult to move and very abrasive are produced. Infrequent or difficult defecation is a common problem in the elderly as ageing is associated with a decline in both secretory activity and motility in the gut. Constipation could develop because of emotional problems, inactive or sedentary lifestyle, lack of fibre and fluid in the diet, intestinal muscle weakness, a neurogenic disorder or an iatrogenic effect. Iatrogenic conditions are those caused by drugs or other medical treatments. 

Constipation is common in the elderly, in people with emotional problems or those with an inactive/sedentary lifestyle, and also with lack of fibre and fluid in the diet, intestinal muscle weakness and neurogenic disorders. 

Symptomatically treatable muscle cramps accompanying various disorders, especially neuropathic abnormalities, are often well controlled with clonazepam [8, 9] (see vignette 8 in Chapter 3). Most muscle cramps are neurogenic, a few are myopathic. Cramps can be caused by a neuropathy that might otherwise be mild. If the neuropathy is worse than mild, it might itself be treatable with IVIG or other anti-dysimmune measure (see below). 

GPC exhibits a broad concentration range in muscles of patients with neurogenic disorders. The diester was increased to 3 nmol in Charcot-Marie-Tooth and Kugelbeig-Welander diseases. Moreover, in muscles of children with meningomyelocele there was as much as 2.1 /tmol of GPC. In contrast, two children with cerebral palsy and one child with amyotrophy after encephalitis possessed only 0.1 and 0.2 / mol GPC, respectively. Amyotrophy of unknown etiology, however, showed normal GPC content (1.6 jumol). This variation in GPC indicates that the nervous system may control lecithin metabolism in muscle, and that diseases of cerebral origin may exert an inhibitory effect on this metabolism. 

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