Cauda equina neuritis, also known as polyneuritis equi, is a rarely recognized noninfectious, chronic relapsing, peripheral neurodegenerative disorder in horses. Cauda equina is latin for 'horse's tail', since it resembles a horse's tail. The disease was initially described in horses in 1897 in Germany. Since than, it has been reported in horses throughout Europe and the United States. It affects the horse's sacral and coccygeal nerves (a bundle of spinal nerves and spinal nerve roots, which are located in the spinal cord), leading to paralysis of the tail, rectum, and bladder. Cauda equina neuritis is found in a variety of horse breeds and ponies with a wide age range. Recent research suggests that cauda equina neuritis may be associated with infection with Sarcocystis neurona, which is the same parasite that causes Equine protozoal myeloencephalitis (EPM). However, the traditional theory for the cause of cauda equina neuritis is that it is immune mediated.

Clinical signs
The most common clinical signs of cauda equina neuritis in horses include hyperesthesia (tail rubbing and hypersensitivity to touch), behavioral changes, prolapsed penis, fecal retention, cystitis, and urine scalding of the limbs. Mild pelvic limb weakness, ataxia, and muscle atrophy in the hind end region may be found.