10 Erb, Ziemssen's Cyclopædia, vol. ix.
It is uncertain whether the nerves supplying the muscles are thrown into morbid action by changes in the muscular fibres and in their sarcolemma, or by simultaneous changes in their own neurilemma. However it arise, irritation of sensory nerve-twigs is present, giving rise to pain, along with irritation of motor filaments, which occasions spasm.
It is probable that the ultimate cause of the irritation within the muscular mass, whatever it is, is common to all cases, and that when myalgia occurs in a healthy man after extraordinary muscular effort or exposure to cold damp when fatigued, or in a delicate child who has played too long, or in a poorly-fed weaver working long hours over his loom, or in the consumptive whose cough gives him no rest, or in connection with any chronic disease or acute disease, whether tonsillitis or bronchitis or fever or rheumatism, it is the same thing—the expression of muscles or groups of muscles overworked. It is not a disease; it is not a symptom of disease. It is an accident of many diseases—of any disease that lowers nutrition. And it is not less an accident of health when such muscular effort is demanded as is beyond the capacity of health.
The essential pathology of myalgia is obscure. It is not an inflammation, as that term is generally understood, but there is ground for the opinion that the lesions are of the nature of a subinflammatory process within the muscle. The not uncommon instances in which an injury or contusion—in short, traumatism—has been followed shortly after the recovery by severe myalgia are of further value as illustrating this theory.
The obstacles in the way of precise histological investigation in cases of acute myalgia are so great that it seems probable that further knowledge is to be reached for the most part by way of clinical work.
DIAGNOSIS.—The fundamental question for consideration in this place is whether we are dealing in any given case with local manifestations of a constitutional disease or with purely local phenomena. That the latter is the correct view seems to the writer to admit of no further discussion in this article. This position being assumed, and due regard having already been paid to the differential diagnosis between myalgia and rheumatism, neuralgia and inflammatory myositis, it seems useless to enter upon the consideration of the diagnosis between this and other painful affections to which it bears but slight and superficial resemblances. Spinal irritation, hypochondriasis, locomotor ataxia, alcoholism, syphilis, gout, and lithiasis are on the one hand attended by pains which are clearly not myalgic in character, and on the other hand peculiarly predispose those subject to them to this affection of poorly-nourished and easily-overworked muscles. Each of these diseases, however, presents a complexus of symptoms in which that which is essential and characteristic is readily to be distinguished from that which—as myalgia—is accidental.
A few words concerning the diagnosis of some of the varieties may not be amiss.
In pleurodynia the ordinary physical signs of pleural, pulmonary, and cardiac disease are absent, the painful points characteristic of intercostal neuralgia are not found, and there is little or no constitutional disturbance.
The diagnosis of myalgia lumbalis is, as a rule, unattended by difficulty. The muscular pain in the loins is characteristic. It is greatly increased by efforts to rise or to turn in bed, and is associated with diffused slight tenderness upon pressure, but never with the acute localized soreness of neuralgia or abscess. The practitioner must, however, guard against the danger of mistaking the back pains of more serious affections for lumbago by the careful examination, in all cases, of the back and abdomen, and by the investigation of the condition of the urine. The possibility that pain in this region may be caused by spinal meningitis, lumbar abscess from spinal caries, sciatica, inflammatory affections of the hip-joint, renal calculus, perinephritis, abdominal aneurism, diseases of the pelvic viscera, and the onset of certain of the acute infectious diseases must not be overlooked.
PROGNOSIS.—Under satisfactory conditions as regards hygiene and treatment the prognosis is always favorable. It becomes in chronic cases unfavorable as regards complete recovery when by reason of poverty, unhealthy occupations, unwholesome surroundings, or established wasting diseases the nutrition of the muscles and their physiological rest are permanently interfered with, and the balance between their power and work permanently deranged.