Paraplegia indicates some disorder of the spinal cord, and consists of paralysis of the posterior half (more or less) of the body. The extent of the disablement will depend upon the seat of the disease, being greater in proportion as it is situated in a forward direction. Injury affecting the spinal cord in the region of the back or loins would paralyse the hindquarters equally or unequally, but if it occurred in the neck, the fore and the hind limbs also, and the rest of the trunk behind the damaged cord, would also be deprived of the power of motion. Paraplegia in the horse is most commonly the result of injury inflicted on the dorsal or lumbar portion of the cord or its membranes, as when from some cause the latter become thickened and unduly press upon the former, or when they contain large quantities of fluid as the result of injury.
Bony growths projecting inwards from the spine sometimes press upon the cord and cause paralysis, or the same results may follow dislocation of the vertebrae.
Rarely spinal paralysis is due to causes originating in organs quite away from the spine, as when mares suffer during oestrum, or foals in consequence of worms in the bowels. This is termed " reflex paralysis", a form of the disease from which animals affected frequently recover. Here uterine irritation in the one case, and intestinal irritation in the other, is the cause of the failure of the spinal cord to innervate the muscles.
In paraplegia there is more or less complete paralysis of the hind-quarters. When it is complete the animal occupies a recumbent posture and is unable to rise. When the skin of the paralysed region is pricked with a pin there is usually no sign of feeling, but in some instances the paralysis may be almost exclusively that of motion, while sensation remains intact, in which case the prick will be felt and expressed by the animal's movements in front. The urine may be discharged involuntarily, and the faeces too may escape in consequence of paralysis of the sphincter ani.
In incomplete paraplegia the hind-quarters roll from side to side, the animal crosses his hind-limbs, sometimes trails the toes, or knuckles over with the fetlock joints. Movement aggravates the symptoms, and may cause the animal to fall, when more or less difficulty or complete inability will be experienced in rising.
Paraplegia in the horse, save when arising out of reflex causes, offers very little encouragement to treatment. Injury to the brain or cord of a paralysing nature seldom yields to medicine. In cases of a slight character it may be desirable to administer a dose of physic, to apply hot cloths over the loins, and to place the animal in slings or on a good bed of peat-moss, and later to administer iodide of potassium and nux vomica for two or three weeks and apply a blister along the back; but these are cases which should be promptly placed under the care of a qualified person.