MUSCLES, Diseases of. Very little is known of the diseases of muscles themselves. Muscle-tissue, in common with other types of tissue, undergoes certain forms of degeneration, fatty, mucoid, gelatinous, calcareous, etc., but of the diseases of the muscular tissues them selves there are few well-defined types. The reason for this lack of definite information bearing on diseases of the muscles is largely due to the close relationship that the nervous system bears to the muscular system. This renders it almost impossible to distinguish be tween a disease of the muscle and a disease of the nerve structures which are distributed to that muscle. Thus, at the present time, it is held that many of the forms of muscular atrophy and some of the forms of muscular dystrophy are forms of the diseases of the nerv ous mechanism of the muscle rather than dis ease of the muscle itself. In former times these were classed as diseases of muscle.
Myositis, simple inflammation of the volun tary muscles, is a form of acute or subacute inflammation in the muscle, due probably to some infectious organism. It is characterized by stiffness of the muscles and with swelling in the muscle-substance. It is usually progres sive, the muscles of the body becoming stiff, hard and fragile, and undergoing fatty degen eration. Myositis is probably a very rare affec tion, and it is not yet known whether it is a primary or a secondary condition. Ordinary muscular spasms or muscular cramps are in reality localized neuralgias in the muscle, and should he considered as of nervous rather than muscular origin. Lumbago is one of the con spicuous examples of a neuromuscular affec tion. It is probably located in the sarcoplasm of the muscle, and results from disturbance of the vegetative nervous system control of the muscle. It may be a result of emotional upsets, or follow undue exercise. Myoclonia or Fried rich's disease, and myotonia, or Thomsen's dis ease, are two forms of disease affecting the muscular system that have certain superficial resemblances to hysterical affections, and al though regarded by many as of purely muscular origin, there are many reasons for believing that these diseases are of the neuromuscular type. In myotonia the disease usually comes
on in childhood; the muscles become stiff, and the children are noted for being clumsy in their movements. The contractions, as in the hand, for instance, commence very slowly and are performed almost automatically, and when the patient desires to loosen his .grasp of an object the muscular response is slow, the contraction often persists or the patient may be scarcely able to open his hand. In much the same man ner walking is affected; the patient starts with difficulty; one leg seems to be stiff and halts; but after a few moments of limbering up, as it were, the patient may be able to walk more or less briskly. The disease is chronic, and is probably related to a defect in the vegetative reflex arc mechanisms acting chiefly through the sarcoplastic elements. It may be emotional but is probably related to faulty muscle meta bolism of endocrinous bases.
Myoclonia occurs chiefly in patients of bad nervous condition, and consists in clonic con tractions of the muscles of the extremities. These contractions somewhat resemble chorea. Associated muscle-groups seem to be involved in myoclonia, whereas in chorea the contrac tions are extremely irregular. The disease is probably most closely associated with the con vulsive tics and is probably due to some affec tion of the motor cortex. Treatment is diffi cult but the psychogenic element may be reached by psychoanalysis.
Myositis ossificans is a very rare chronic affection of muscles, during which the muscles become harder and harder, and finally develop bone-like transformations, so that the patient becomes like the ossified man of the circus. As a matter of fact most of these cases drift into museums and circuses. Very little is known as to the cause of the disease, and treatment is unavailing. Consult Jelliffe and White, 'Dis eases of the Nervous (3d ed., 1919).