CHOREA. ST. VITUS DANCE.
Definition. Susceptible animals. Causes: nervous lesions inconstant, youth, debility, anæmia, microbian toxins, cerebral embolism, rheumatism, trophic alterations in nerve cells, fright. Lesions: variable in seat and character, congestion of perforated space, corpus striatum, Sylvian convolutions, gray matter at root of posterior horn of spinal cord, etc., experiments of Chauveau and Wood. Symptoms: dog, local twitching, fore limb, one or both, neck, head, maxilla, eyelids, eyeballs, hind limbs, trunk, rhythmic, less when recumbent, usually absent in sheep, roused by excitement: horse, head neck, fore limb, trunk: cattle, head, neck, limbs: swine, hind limbs, neck, head: severe cases lead to exhaustion, emaciation, marasmus, paralysis. Duration: weeks, months, years. Treatment: laxative, tonic, hygienic, arsenic zinc sulphate, strychnia, sedative, belladonna, conium, cannabis Indica, chloral, acetanilid, trional, etc., icebags or ether spray to spine, cold douches, outdoor life.
Definition. A neurosis characterized by constant twitching of muscles or of groups of muscles, and which usually ceases during sleep.
Animals Susceptible. This disease is especially common in the dog, but has been recognized also in the horse, ox, cat and pig.
Causes. Much difference of opinion exists as to the true cause of chorea. In many cases no nervous lesion has been found and therefore the disease has been pronounced purely functional. The victims are as a rule the young, weak and debilitated so that anæmia has been held to be the main causative factor. Then in dogs the affection is a common sequel of distemper and hence it has been attributed to toxic matters (microbian, etc.) in the blood. It should be added that European writers attribute the rhythmic spasms which follow distemper to eclampsia, epilepsy or tic, and claim that the contractions must be irregular or arhythmic in order to constitute chorea. English and American writers, however, have attributed less importance to this point and consider that the constancy and persistency of the contractions in the dog, differentiate an affection from both eclampsia and epilepsy and relate it rather to chorea. Tic as illustrated in cribbiting is certainly not constant nor rhythmical nor is it a habit beyond the control of the will.
Among other alleged causes of chorea is embolism of the arteries of the brain or spinal cord. Angel Money went so far as to inject a fluid containing arrowroot, starch granules and carmine into the carotids of animals, and produced movements closely resembling those of chorea. Another theory connects chorea with the rheumatic poison. Some English writers find more than 80 per cent. of all cases in man associated in some way with rheumatism, but in Philadelphia, Sinkler found that not more than 15 pet cent. showed such a relation. D. C. Wood as the result of necropsies of a number of choreic dogs reached this conclusion: “Owing to emotional disturbance, sometimes stopping of various vessels of the brain, or sometimes the presence of organic disease, there is an altered condition of the ganglionic cells throughout the nerve centres. If the cause is removed and the altered condition of the nerve cells goes only so far, it remains what we call a functional disease. If it goes so far that the cells show alteration, we have an organic disease of the nervous system.”
In man the element of sudden fright is awarded a high position in the list of causes.
Lesions. Constant morbid changes of structure have not been established in chorea. On the contrary in the many careful necropsies of choreic subjects some lesion of brain or spinal cord has been almost always found. Dickinson always found congestion of some part of the brain or spinal cord, but most constantly of the substantia perforata, the corpora striata and the beginning of the Sylvian fissure. In the cord the cervical and dorsal regions were the most commonly affected, and preëminently the gray matter at the root of the posterior horn. The bilateral symmetry of the contractions in cases of unilateral lesions, has been held to discredit the theory of embolic origin, yet this may be explained by mutual relation of the ganglia of the two sides and their coördination of function.
The question of the relative importance of the encephalic and spinal lesions has been also debated. Chauveau believed that by section of the cord in choreic dogs, he had proved that the spasms were of medullary origin. Wood on the other hand found that the choreic movements persisted after section of the cord, and seemed warranted in the conclusion that the movements originated in the cord. The probability is, that with the cord intact, the primary source of the morbid movement may reside either in the encephalon or the cord. In chorea, following distemper, I have found marked congestion of the encephalon and its meninges.
Symptoms. In the dog the twitching may be confined to one fore leg, or it may extend to both and then usually implicates the neck and head. In other cases the lower jaw, the head, the eyelids or even the eyeballs may be the seat of the twitching motions and in still others the hind limbs and trunk are also implicated. In nearly all cases the tendency is to a continuous rhythmic action, which may moderate without actually ceasing while the animal lies down, but which usually stops altogether during deep sleep. When it intermits at other times it can commonly be roused into activity by exciting the animal in any way.