Cauda Equina Syndrome in Horses

In the roll call of neurological diseases from which horses can suffer, there is one many horse owners don't yet know about--cauda equina syndrome. Caused by myriad infectious, inflammatory, and/or traumatic factors, the syndrome includes many hind-end neurological clinical signs stemming from damage to the cauda equina, the tapered end of the spinal cord along with the extensions of spinal nerve roots extending alongside and past it. Scott Pirie, BVM&S, PhD, CertEP, CertEM, MRCVS, described cauda equina syndrome in depth at the 2004 British Equine Veterinary Association Congress, held Sept. 15-18 in Birmingham, U.K.

Postmortem specimen of the cauda equina region from a horse with cauda equina neuritis (polyneuritis equi). As a result of the inflammation associated with this condition, the sacrococcygeal spinal nerve roots (one of which is highlighted), seen emerging from the dura covering the terminal spinal cord, are markedly swollen.

Courtesy Professor I.G. Mayhew

"The cauda equina is so called due to its gross resemblance to a horse's tail," he began. "The most common clinical signs of cauda equina syndrome include tail paralysis/weakness, anal hypotonia/atonia (poor or no muscle tone), rectal and bladder paralysis/weakness, and relaxation and protrusion of the penis. Other signs include lack or absence of skin sensation (hypalgesia or analgesia) of the tail, anus, and skin of the perineum; and muscle atrophy of the coccygeal muscles (which control tail movement). Occasionally, hindlimb weakness, ataxia, and muscle atrophy have been associated with damage at the more cranial (forward) aspect of the cauda equina region. Less common signs are pelvic limb/rump muscle weakness and atrophy. Subtle signs might include reproductive dysfunction such as impotence, urospermia (urine ejaculated in semen), and urine pooling in mares.

"The signs observed depend on the site of the damage," Pirie explained. "There is usually no major gait abnormality if there is minimal involvement of the lumbosacral nerve roots."

Cauda Equina Causes

Trauma to the sacral/coccygeal area is the most common cause of the syndrome and can result from falls, reversing under obstructions (such as backing under a closed top door to a stall), and tail pulling such as occurs when using the tail to help pick up a down horse. "The deficits are usually immediate, but beware of delayed signs, which can be caused by unstable fractures, hematomas (bruises), or abscesses," Pirie noted.

Neuritis (nerve inflammation) of the cauda equina is rare and causes an insidious (gradual), progressive onset of clinical signs, he said. Other non-traumatic causes he described include:

  • Vertebral osteomyelitis (epidural/paravertebral abscesses, such as from Rhodococcus equi infection in foals);
  • Equine herpesvirus-1 (EHV-1), myeloencephalitis (acute onset, rapid progression, and stabilization with limb weakness/ataxia, respiratory signs, and preceding fever);
  • Occasionally equine protozoal myeloencephalitis (EPM);
  • Epidural neoplasia (abnormal growth of cells within the spinal canal);
  • Rabies;
  • Caudal meningitis;
  • Verminous myelitis; and
  • Sorghum/sudan grass toxicity.

Diagnosis of cauda equina syndrome is by physical examination and additional findings of infectious, inflammatory, or traumatic causes (i.e., finding an infectious organism known to cause the syndrome or fractures via diagnostic imaging). Analysis of the cerebrospinal fluid at the lumbosacral site can also shed light on the cause.

Some causes of the syndrome can also damage neurons at other sites, thus causing additional clinical signs.


"Treat the underlying cause where appropriate--medications for EPM, fixation for fractures, etc.," Pirie recommended. Non-specific treatments include non-steroidal anti-inflammatory medication; and supportive nursing care, including bladder drainage/lavage, prophylactic antibiotics to decrease cystitis (bladder infection), topical skin treatment to prevent urine scald, manual fecal removal, and fecal softeners. "Prognosis is largely dependent on the initial cause of the syndrome," he concluded.


About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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