This section is from the book "The Farmers Ready Reference Or Hand Book Of Diseases Of Horses And Cattle", by S. C. Orr. . Also available from Amazon: The Farmer's Ready Reference;.
Chorea is a disease of the nervous system characterized by involuntary twitchings of the muscles. There are several forms of the disease of which a short description of each will be given.
Stringhalt. This is the most common form and is easily recognized by every horseman by the sudden jerking-up of one hind leg when first starting out; sometimes both hind legs are affected There are some cases in which it is not noticeable when the animal goes forward, but if you try to back him or turn him quickly he will jerk his feet. And in some instances if you try to back him he cannot move, but his tail will be elevated and his muscles will become rigid; hence it is always well to try a horse thoroughly before purchasing him
Immobility. In this form of the disease the horse may appear all right while in the stable or moving about the yard and he may travel several miles upon the road all right, when suddenly and without any apparent cause he begins to go lame and in a short time goes down unable to proceed. After a few hours' rest, however, he generally gets up ready to continue his journey until another attack comes on. This form of the disease, fortunately, is very rare.
Shivering. This is of more frequent occurrence than the last form. A horse with this form is called a shiverer. He may be standing quiet and the attendant strikes him or even speaks sharply and he will exhibit an uncontrollable shivering and twitching of the muscles, which lasts until the excitement passes off. I have seen another form closely allied to this last, but with symptoms very similar to an aggravated case of St. Vitus' dance in the human family.
Treatment - Although it is known to be due to a diseased condition of some part of the nervous system yet it is difficult to determine just what nerves are affected; hence treatment has not generally been successful. There is no known treatment which a novice can apply with success. The disease is hereditary beyond a doubt and animals thus affected should never be used for breeding purposes.