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.
In the horse the muscles affected may be those of the head and neck, of
the fore limb (Hering), of head, limbs and trunk (Leblanc).
In cattle the movements have affected the neck and head and the fore or
hind limbs (Anacker, Schleg).
In young pigs the hind limbs, the neck and head have been chiefly
involved in the spasms (Hess, Vervey).
If the affection is slight it may not seriously impair the general
health, but in proportion to its severity and the constancy and
generalization of the spasms and the consequent muscular waste and
exhaustion, the animal becomes gradually worn out and emaciated and dies
of paralysis and marasmus.
_Duration._ In favorable cases recovery may ensue in a few weeks; in
others the disease becomes chronic and will last for months or years.
_Treatment._ Among the first indications are fresh air and wholesome
easily digestible food. The removal of any source of intestinal
irritation should be sought by bland laxatives. As the health is usually
low, a course of iron tonics is nearly always in order.
Special nervous tonics are next demanded. No agent has a better
reputation than arsenious acid. Ten drops of a 1 per cent. solution of
arsenite of soda may be given daily to the dog or one ounce to the
horse. If gastric irritation forbids the use of this agent, sulphate of
zinc may be given in 1 to 3 grain doses twice a day to the dog. In other
cases strychine ¹⁄₈₀ to ¹⁄₆₀ of a grain may be given in the same manner.
Nerve sedatives often have a good effect in calming the nervous
irritability and in this way belladonna, conium, cannabis Indica,
chloral, chloroform, acetanilid, trional, etc., have been employed.
In the same line are ice bags or ether spray applied to the spine for
ten minutes at a time, and douche baths of cold water, the animal being
afterward rubbed dry. This last partakes of the nature of a stimulant
and may be classed with gentle exercise which at once distracts the
patients’ attention from the nervous infirmity, trains him to control
the muscles, gives normal exercise and tone to the enfeebled organs and
improves the general health.