CAUDA EQUINA SYNDROME
Degenerative lumbosacral stenosis generally involves a compression of the nerve roots in the lower back. Most dogs affected by lumbosacral degeneration are middle aged or older members of the larger, athletic breeds. As a rule, these breeds are very tolerant of discomfort until it eventually overrides their character and results in clinical manifestations.
The most common, and often the only, symptom is progressive sharp pain. However, this syndrome can manifest itself in a number of ways. Intermittent lameness in one or both pelvic (rear) limbs or a stilted gait is a common initial sign. The patient may progressively have more difficulty rising from a prone position or may be unusually reluctant to leap. The dog may act suddenly (but often transiently) painful or lame immediately after getting up or jumping. Strenuous activity may exacerbate the signs. Vocal expression of pain may vary from moans or whimpers when the dog tries to rise, to sharp cries to howls when touched over the rear quarters or making a wrong move during exercise. Eventually, even the most stoic (pain tolerant) individuals will react to the exquisite, burning pain of the nerve root entrapment caused by this syndrome. Chewing at the tail or rear feet and bowel and bladder incontinence may be seen in advance cases where severe pressure of the nerve roots causes the burning sensation described as "sciatica". The most devastating cases can evolve to full paralysis.
The neurologic examination begins by observing the gait. Specific test for pain and neurologic dysfunction are then performed to confirm the site of the lesion.
Individual with hip dysplasia will often show a mild response to hip extension, whereas dogs with lumbosacral disease will object more acutely to hip extension and cry when pressure is added to the lumbosacral junction (Fig.1). Manipulation and hyperextension of the tail causes an exquisite pain response. The spinal reflexes are tested, including the perineal reflex and anal tone, to assess the early signs of nerve root entrapment that lead to incontinence.
Nerve root entrapment and pressure can result from an arthritic process, infection, a degenerative disc rupture, or tumors. Therefore, it is essential to accurately diagnose your pets individual problem before considering treatment (Fig 2&3). This requires radiography (x-rays).
Plain radiographs can be taken under general anesthesia and are very difficult in diagnosing syndromes such as infection, trauma, severe arthritis or bone neoplasia. A definitive diagnosis may require special x-ray tests. A myelogram or epidurogram (contrast dye studies of the spine) are used to confirm and document not only the location of the lesion but also the dynamic position of the ruptured disc in relation to entrapped nerve roots as the spine is flexed and extended. With new gas anesthetics, advanced monitoring equipment, and modern "contrast" agents for the dye study, the myelogram and epidurogram are now common and safe diagnostic procedures when performed under the proper conditions. In difficult cases, MRI or CT scans are available and are of exceptional diagnostic value. Electromyography (EMG) may be of value in substantiating the diagnosis and the severity and symmetry of nerve root entrapment.
Medical therapy (consisting of rest and anti-inflammatory/ analgesic medication) should be tried in patients with the first episode when experiencing mild pain only.
Indications for surgical intervention include neurologic deficits, pain unresponsive to proper conservative treatment, and frequent recurrences to pain, even if the episodes respond well to medical treatment. To relieve pressure on the entrapped roots a dorsal laminectomy is performed. This involves removing portions of the bony canal entombing the entrapped nerve roots. This conservative laminectomy adequately exposes the nerve roots and allows the surgeon to safely retract them for exposure of the disc space. The cauda equina is gently retracted to one side with blunt nerve hooks, exposing the herniated discs as a large dome on the floor of the spinal canal. The herniated disc is excised, compressive osteophytes removed, and formenotomies (opening the nerve root canals) performed to relieve root entrapment. Once the pressure s relieved, the neurologic function gradually returns as the nervous tissue heals in its decompressed environment.
A course of rest is the most important component of postoperative care. All strenuous and acrobatic activity should be curtailed for at least 6 weeks. At that time, the exercise level is gradually increased. If the dog is obese, weight should be reduced.
The prognosis depends on the severity and chronicity of clinical signs before surgery. Dogs with pain, reluctance to jump, or tenderness upon getting up as their only symptom will usually improve rapidly and dramatically. Some patients may have an occasional, transient painful episode. Dogs with chronic neurologic dysfunction will take much longer to improve, and they may never return to completely normal function. However, at the very least they will return to a pain free lifestyle.
Copyright 1998, Southern
California Veterinary Surgical Group