Cervical Intervertebral Disc Disease

Intervertebral discs are the cushioning structures located between the vertebrae of the spine. Over time, various conditions and mechanical forces can cause these discs to swell, degenerate, or rupture. When a disc ruptures, it can damage the spinal cord in two primary ways: by direct compression and by concussive injury. The severity of spinal cord damage and the extent of nerve cell loss depend on several factors, including:

• The type of force involved
• The magnitude of force exerted on the spinal cord
• The duration for which the force is applied

Mild injury to the spinal cord may result in incoordination and an unsteady, “drunken sailor” gait. More extensive damage can lead to an inability to walk or to voluntarily move the limbs. In the most severe cases, pain perception is completely lost, a finding that is associated with a very poor prognosis for recovery, particularly when the loss of pain sensation has been present for an extended period.

Chondrodystrophoid breeds—such as Dachshunds, Pekingese, Beagles, and Lhasa Apsos—account for the majority of intervertebral disc ruptures, with Dachshunds alone representing approximately 45–70% of all cases. In these breeds, clinical signs typically begin between 3 and 6 years of age, although radiographic evidence of disc calcification may be present as early as 2 years of age. Non-chondrodystrophoid breeds, including Labrador Retrievers and German Shepherd Dogs, usually develop disc disease later in life, between 5 and 12 years of age. Disc ruptures most commonly occur in the thoracolumbar region (back), accounting for about 65% of cases, while cervical disc ruptures (neck region) make up as much as 18% of presentations.

Intervertebral disc rupture causes varying degrees of pain. As neurologic damage develops and worsens, clinical signs tend to progress in a predictable sequence:

• Pain in the back or neck, sometimes severe enough that the pet refuses to walk or move around
• Loss of coordination, with a wobbly or “drunken sailor” gait; the hind feet often cross while walking
• Complete loss of voluntary motor function in the hind limbs, frequently accompanied by inability to urinate normally or to fully empty the bladder
• Loss of pain perception, indicating severe spinal cord injury and a guarded to poor prognosis

Neurolocalization

Disc ruptures are categorized based on the region of the spine involved, using the following groupings:

• Cervical vertebrae 1–5 (C1–C5)
• Cervical vertebrae 6 through thoracic vertebrae 2 (C6–T2)
• Thoracic vertebrae 3 through lumbar vertebrae 3 (T3–L3)
• Lumbar vertebrae 4 through the sacrum (L4–S3)

This classification system, known as neurolocalization, helps an ACVS board-certified veterinary surgeon determine appropriate diagnostic tests and potential surgical options. Intervertebral disc rupture is generally considered a true surgical emergency, and prognosis varies widely depending on the neurologic function present at the time of evaluation and treatment.

Initial evaluation by a primary care veterinarian often includes general health screening and may involve one or more of the following diagnostic tests:

• Blood tests, including complete blood count (CBC), serum biochemistry, and urinalysis
• Radiographs (x-rays) of the spine or chest
• Myelography, in which contrast dye is injected around the spinal cord to identify areas of compression (Figure 1)
• Computed tomography (CT), either instead of or following a myelogram
• Magnetic resonance imaging (MRI), used in addition to or instead of CT
• Cerebrospinal fluid collection (spinal tap), often performed at the time of imaging

The choice of diagnostic tests depends on the individual patient and is determined by the veterinary surgeon.

Conservative treatment—consisting of strict confinement, cage rest, and pain medication—is generally reserved for pets experiencing their first episode of disc disease with only mild neurologic deficits. In many cases, referral to a veterinary surgeon is recommended to fully evaluate all treatment options.

A variety of surgical techniques and approaches are available, depending on surgeon preference and the location of the affected disc. The specific procedure selected is based on the surgeon’s experience and the individual case. In most situations, surgical decompression of the spinal cord is strongly recommended. This is achieved by removing a portion of the vertebral bone overlying the spinal canal (such as a hemilaminectomy) to allow removal of herniated disc material (Figure 2).

Most patients are discharged from the hospital within 3–7 days after surgery and return for follow-up examinations and removal of skin sutures or staples if present. Postoperative pain is usually well managed with medications administered by the owner at home.

Recovery following surgery may involve:

• Manual bladder expression 3–4 times daily, if necessary
• Physical rehabilitation to improve muscle strength and flexibility
• Strict exercise restriction (“bed rest”) for at least 4 weeks
• Lifestyle modifications, such as weight reduction, use of a body harness instead of a neck collar, and limiting jumping on and off furniture

Possible postoperative complications include:

• Seizures within the first 24 hours following a myelogram
• Infection at the surgical incision site
• Development of additional disc herniations later in life, with an estimated recurrence rate of approximately 25%
• Persistent gait abnormalities, such as wobbliness or dragging of the hind toes

Prognosis depends greatly on both the severity and location of the spinal cord injury. In dogs that retain pain perception, surgical treatment allows approximately 90% to regain limb function, although some residual incoordination may persist. With strict medical management alone, about 60–80% of these dogs may recover function. In contrast, for dogs that have lost pain perception entirely, surgical treatment results in recovery of limb function in approximately 50–60% of cases, while medical management alone leads to recovery in fewer than 10%. Overall recovery from intervertebral disc disease can be prolonged, often taking weeks to months, with surgical recovery generally being faster than recovery achieved through medical management alone.

Dogs that lose hind limb function may also lose the ability to urinate normally. If neurologic function improves, voluntary urination may return. Until then, owners must manually express the bladder several times daily. These patients are at increased risk for chronic urinary tract infections and urine scalding. Additionally, immobile pets are prone to pressure sores and skin wounds because they cannot reposition themselves. Providing soft, well-padded bedding can help reduce this risk. Some dogs may develop abnormal tingling sensations (paresthesia), which may resolve over time or persist and lead to self-trauma.