Acute inflammation of the coverings of the spinal cord is of seldom occurrence, and mostly involves the two innermost membranes - the pia mater and arachnoid.
The causes which give rise to this disease are for the most part the result of injury, but it may also follow upon exposure to cold easterly winds and wet, especially in the case of a horse that is heated after a fast run with hounds and much jumping, or after a period of heavy draught. Tumours in the spinal canal, and the bursting of abscesses into it from disease of the vertebras, may also occasion it.
These will vary in severity, according to the intensity of the cause. They may either be sudden and severe in their onset or slowly progressive. In the former case the disease is ushered in by rigors or shivering, followed by paroxysms of pain in the course of the spine, exhibited more especially when the animal is made to move. Later, sudden and repeated fits of spasmodic contraction of the muscles of the limbs appear, causing them to be suddenly jerked upward and forcibly brought to the ground. The movements become unsteady and the fetlocks knuckle over, the patient loses the power to stand, and sooner or later becomes completely paralysed. When on the ground he makes repeated attempts to rise, during which there are violent fits of struggling and painful spasms of the muscles of the limbs and back.
During these paroxysms the face wears a drawn and anxious expression, deep groans are emitted, the breathing becomes hurried, the pulse quickened, and sweat covers the body. Short intervals of ease follow the convulsive seizures, but growing muscular weakness, followed by complete paralysis of both motion and sensation, sooner or later ends in disablement or death.