The cauda equina is made up of the tail end of the spinal cord and the adjacent nerve roots. Sometimes the spinal canal, through which the spinal cord and nerves pass, narrows and then compresses the nerves. The most common spot for this narrowing to occur is at the lumbosacral joint, where the spine meets the pelvis. Spinal canal narrowing at that joint is referred to as lumbosacral stenosis, and the condition resulting from these compressed spinal nerve roots is called cauda equina syndrome.
Alternatively, in another cause of cauda equina syndrome, the foramina (the holes through which the spinal nerves exit) become narrowed and compress the nerves either permanently or intermittently.
The narrowing within the spinal canal is most often caused by arthritic degeneration or intervertebral disc herniation, but traumatic injury, congenital malformation (born with it), or tumor growth can also be involved. Narrowing of the foramina can be caused by new bone growth, the spurs that grow as a result of arthritis, or by overgrown soft tissue from the capsule surrounding the joints.
The most common symptom of lumbosacral stenosis is pain. In the beginning you may notice your dog has hind end stiffness that leads to difficulty in walking, climbing stairs, getting on furniture, wagging the tail, positioning to defecate, or getting into a car. As the condition progresses, one or both back legs may become weak. Some dogs will cry out in pain when trying to move. In severe cases, the nerve roots can become so compressed that urinary and fecal incontinence will result. Trapping of the nerves can also cause intermittent pain, depending on the dog’s position.
German shepherd dogs and other large, active breeds are most commonly affected. However, it can also be seen in smaller breeds and even in cats. It is unusual to see signs in dogs younger than 3 to 7 years old.
The first diagnostic test is a physical and neurologic examination. A veterinarian observes the dog's walk and then tries to determine where the pain is located. Additional diagnostic tests are usually required to establish the diagnosis. These include x-rays, CT scans, MRI, and rarely electromyography, a diagnostic procedure that evaluates the health of the muscles and the nerve cells that control them. Traditionally, a myelogram, a specialized x-ray where contrast liquid is injected into the spinal canal to outline the narrowed areas, was the preferred test. More recently, advanced imaging techniques - especially MRI - have become the tests of choice. MRI is now essential in allowing treatment, especially surgery, to be planned.
Treating lumbosacral stenosis depends on the cause and severity of the symptoms. Mild cases often need only supportive treatment, including crate rest, controlled exercise on lead, and anti-inflammatory and pain-relieving medications.
If symptoms persist or worsen, or if neurologic signs develop, it may indicate a need for surgery. A dorsal laminectomy creates an opening in the top of the spinal canal to relieve pressure from the nerves. Occasionally, adjacent unstable spinal vertebrae may have to be fused to prevent recurrent nerve trauma. If the foramina are narrowed, these may also need to be widened. These can be done in the same surgery.
Strict rest in the post-operative period is essential to minimize complications.
The best approach is to start with medical treatment and leave surgery as a last resort if there is no improvement or if neurologic signs are developing. That’s more the case currently than ever before now that corticosteroid injection is an option.
Dogs with mild signs have a good prognosis as they can be medically treated. Severely affected dogs, including those whose nerve root compression is so severe that urinary or fecal incontinence has resulted, have a poor prognosis as most such dogs do not become continent again, even after surgery. However, surgery or epidural cortisone can relieve pain and improve quality of life.