Rheumatism is a specific constitutional disease, sometimes assuming an acute febrile character. It is specially marked by local manifestations of pain of varying degrees of intensity, with a tendency to shift from place to place, and to recur periodically. Horses of all ages are liable to it, but it is most prevalent in the aged.
Heredity is undoubtedly a factor in the causation of rheumatism, and, as in gout, the disease would appear to be due to some incomplete elaboration of the nutrient elements of the food, whereby a. rheumatic poison is generated in the body and brought into activity by certain extraneous causes. Among these may be mentioned unsanitary surroundings, cold, damp, and vitiated stables, and damaged fodder. Any condition tending to reduce an animal's vitality or bring him below " par" increases his susceptibility to attack. Seasonal influences, as exposure to the biting east winds of spring and autumn, are often accountable for attacks of this disease in susceptible subjects. Horses brought from a hot stable and then, while heated, compelled to stand without clothing, exposed to wet and cold, readily contract the disease. Animals subjected to habitual exposure, but without those sudden alternations from the warmth of the stable to the draughty street corner, are much less liable to contract the disease than the animals living in hot stuffy stables.
Rheumatism may present itself as an acute fever with manifestations of local pain, or it may assume a chronic and less severe character.
In the former case the animal shows marked indications of constitutional disturbance, notably a high temperature, quick pulse, increased breathing, hot skin, injected eyes, inappetence, and constipation of the bowels. Locally, the disease may centre itself in one or another of the joints of the extremities, or in the tendons and ligaments of the limits, or in the muscles. Whichever structure is involved, the part becomes more or less swollen, hot, and intensely painful, so much so that the upright posture is maintained with difficulty, and only at the expense of considerable suffering. The disease may be confined to one extremity only, or it may involve two or more. In the chronic or sub-acute form of the disease there is seldom any obvious disturbance of the system, the pulse, breathing, and temperature remain normal, and the appetite is undisturbed. The disease mostly attacks the limbs, but may also implicate the muscles of the loins, producing lumbar rheumatism or lumbago. The seat of attack may or may not be enlarged, but more or less heat and tenderness is generally observed in it. When swelling of the structures appears it is usually firm, and seldom altogether disappears. The pain and lameness is liable to vary in severity from day to day, and to shift from part to part, and from limb to limb, so that the lame leg to-day may be the sound one to-morrow, and vice versa. An animal once affected with rheumatism seldom escapes a second attack, and the liability to recurrence of the disease becomes greater as time goes on. Many of those large swellings found on the limbs of horses involving the bones are of rheumatic origin, as are also others seen in the tendons and ligaments of the legs. The joints of horses are frequently found to become gradually enlarged by repeated attacks of the disease.
The reduction of temperature in those sudden and acute attacks of rheumatism referred to is of first importance, and this should be attempted by the administration of successive doses of salicine. The salicylate of soda is perhaps the most useful salt in rheumatic affections, and doses of 4 to 8 drams are not considered excessive. If the heart is weak and too easily depressed, salicylic acid may be preferred as having less action upon that organ. This treatment may be accompanied by a mild aperient, preferably of a saline nature, as sulphate of magnesia or soda, and if the symptoms do not rapidly abate salicylates may be exchanged for iodide of potassium, with bicarbonate of potash or soda in the drinking-water. The diet should not be stimulating, and if the allowance of corn has been full it should be considerably reduced. Where very acute pain is evinced it may be desirable to place the patient in slings, and to employ anodynes both internally and to the swollen parts (see section on anodynes). Hot fomentations and bandages to the inflamed parts, friction with the hand, aided by liniments of soap and iodine, also afford considerable relief.
Recurrent rheumatism at particular periods, as in moulting and during the prevalence of east winds, may be combated in advance by a course of soda or potash and a laxative dose of medicine a little while before the usual time of attack. Good drainage, a dry stable, and plenty of dry bedding are particularly desirable for horses that have been previously subject to rheumatism.