Sedentary occupations, leading as they do to poor nutrition of the muscular system from want of proper use and exercise; malnutrition from a diet deficient in amount or defective in kind, or in childhood from too rapid growth; the chronic wasting diseases; the state of convalescence from acute maladies; and, finally, degenerative diseases of the muscles themselves,—all favor the development of myalgia. Among the acute diseases which by their derangement of nutritive processes especially render those who have suffered from them liable to this painful affection of the muscles during convalescence, is acute articular rheumatism or rheumatic fever. It is this fact, taken together with the use of a misnomer, that has given rise to the view that the muscles share with the serous and fibrous structures in the lesions of that disease, and that myalgia is rheumatism of the muscles.
There is, however, over and above these defects in nutrition, an especial predisposition or idiosyncrasy, the nature of which is unknown, which renders certain individuals far more liable to suffer myalgic pain than others. This predisposition is encountered in those who have an inherited or acquired gouty habit and in those who are free from gout with perhaps equal frequency. It is not associated with a special liability to true rheumatism.
(B) Exciting Causes.—Myalgia is a local affection, and depends for its causation upon a derangement of the balance between the nutrition of the affected muscles and the work they have been called upon to do. Hence the most common exciting cause is (a) overwork pure and simple, especially overwork which brings into excessive and prolonged exercise unaccustomed muscles. Next in frequency is (b) exposure to cold, and especially to damp cold, when overheated or overfatigued. Finally (c), inevitable and incessant contractions, such as are physiological and are performed without consciousness or sensation in a healthy state of the muscles, will, in muscles that are defectively nourished or have undergone fatty, granular, or fibroid degeneration, cause more or less distinct myalgia.
As examples of myalgia due to the first of this group of causes (a) I may cite the pain in the adductors of the thighs after a hard ride when out of practice; the epigastric pain in children suffering from measles or other acute affection attended with persistent cough; and the pain of spasm, in particular that which follows tonic spasm, such as occurs from reflex causes in the calves of the legs at night and in bathers. Many of the pains of childhood, which are classed in common parlance together under the name of growing pains, are myalgic in their nature.
Examples of the second form (b) may be instanced in the pains of wry neck or lumbago, such as often occur in those who, being very tired, but otherwise healthy, fall asleep in a draught of air, or in those who, coming home at evening in cold weather, find a leaking pipe in the cellar, and stooping over to stop it, or in some other emergency of every-day life, bring into excessive use unaccustomed muscles in an atmosphere that is at once cold and damp.
Examples of the third group (c) are common enough in the flying or fixed muscular pains and soreness that occur in wasting chronic diseases and in the convalescence from acute maladies when prolonged muscular effort is too early undertaken. Certain forms of præcordial pain that occur in degenerative lesions of the muscular substance of the heart are without doubt myalgic in character, and will, when the clinical data of such conditions come to be more fully understood, be recognized as having more or less diagnostic value.
SYMPTOMATOLOGY.—The chief symptom, the one symptom that is common to all the cases, is pain. It is sometimes, especially in acute cases, constant; more frequently it is very slight or wholly absent when the patient is at rest, with the affected muscles in full extension, but it is invariably present or aggravated when the muscles are called into action. It is experienced throughout the muscular mass, but is most intense at or near the point of tendinous insertion. Its character is usually stabbing or stitch-like, but prolonged; sometimes it is acutely dragging or tearing; in others it is like the soreness felt on moving a contused or inflamed part. It is frequently in acute cases, almost always in chronic cases, accompanied by a sensation of stiffness in the affected muscles. The pain is essentially the same in all cases, variations in its character and severity being determined by the opportunities afforded the muscle for physiological rest. It is in accordance with this statement that the most obstinate, and the most severe form of myalgia is that which occurs in the intercostal muscles and their fibrous aponeuroses—pleurodynia. Here the affected muscles are constantly concerned in the movements of respiration, and have no time for physiological rest except in the intervals of those movements. Scarcely less stubborn and severe are the myalgias of the great muscular masses, of which the principal function is to maintain by their nicely-balanced and ever-varying contractions the erect position of the head and trunk. Less painful and of shorter duration are the myalgias of the limbs—less painful because prolonged intervals of absolute rest may be voluntarily secured; of shorter duration, because it is by rest that the balance of the nutrition is most speedily restored.
There is usually some degree of tenderness over the whole extent of the myalgic area, becoming more marked in the regions of tendinous insertion, to which it is, however, in many cases restricted. It is elicited upon moderately firm pressure, and is not associated with cutaneous hyperæsthesia.
Spasm is absent in the acute cases, except when the muscles are brought into use. Its occurrence has much to do with the intensity of the suffering then caused: in chronic cases a condition of tonic spasm or spastic rigidity, with more or less persistent painfulness, comes on, and finally in very chronic cases such tissue-changes take place as result in great impairment or absolute loss of contractile power, with or without atrophy.