What Is Cauda Equina Syndrome?

Reviewed by: HU Medical Review Board | Last reviewed: February 2019 | Last updated: September 2020

Cauda equina syndrome is a rare but potentially serious complication that can occur in people with ankylosing spondylitis (AS).1 "Cauda equina" means horse tail, and the syndrome is named for the collection of nerves and nerve roots at the base of and just below the spinal cord which have a similar appearance to a horse's tail. In cauda equina syndrome, or CES, these nerves at the bottom of the spine become compressed. These nerves send and receive messages from the organs in the pelvis and the legs, and when they are compressed, it can lead to motor and sensory problems for the legs, bladder, and bowel control.2,3

How can AS cause cauda equina syndrome?

In people with AS, chronic inflammation can damage the spine, leading to excess bone formation along the vertebrae of the spine. Some people develop spinal stenosis, a narrowing of the spinal column, which can pinch the nerves that come out from the spinal cord. CES is a severe form of spinal stenosis at the base of the spine.4

CES can also be caused by a tumor on the spine, severe infection, or spinal fractures from osteoporosis.2

Symptoms of cauda equina syndrome

The nerves of the cauda equina are responsible for motor and sensory function to the legs and bladder. When these nerves become compressed due to CES, it can cause a loss of bladder or bowel control or paralysis in the muscles of one or both legs. The paralysis may be permanent.2

Symptoms of CES can include2,3:

  • Severe low back pain
  • Loss of bladder control (incontinence) or urinary retention (inability to completely void bladder)
  • Loss of bowel control (bowel incontinence)
  • Weakness or sensory loss in both legs
  • Difficulty walking
  • Loss of or reduction in reflexes in the legs
  • Loss of feeling in the areas that would sit on a saddle (saddle anesthesia), such as the buttocks, the inner thighs, and the back of the legs

Symptoms of CES can vary in their severity, depending on the degree to which the nerves are compressed or which nerves are affected. Symptoms may begin gradually and increase over time.2

How is cauda equina syndrome diagnosed?

CES may be difficult to diagnose, as it is rare and early symptoms may be similar to those from other conditions. Diagnosis may be determined using a physical examination, blood tests, and imaging, such as a magnetic resonance imaging (MRI) scan or a myelogram, a test that uses a liquid dye and x-ray or computerized tomography (CT) scan.2

How is cauda equina syndrome treated?

CES is a medical emergency. Prompt treatment of CES is important to improve sensory and motor function of the legs, bladder, and bowel. If left untreated, permanent paralysis, loss of sexual sensation, or permanent loss of bladder or bowel function can occur. Treatment within 48 hours after the onset of symptoms can help ensure the damage is not permanent. Treatment involves surgery to reduce or remove the pressure on the nerves.1,2

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