Thoracolumbar Intervertebral Disc Disease

Intervertebral discs (the cushioning structures located between the bones of the spine) are exposed to conditions and mechanical forces that, over time, can cause them to bulge or rupture. When a disc ruptures, it can injure the spinal cord in two main ways: compression and concussion. The severity of injury and the degree of nerve cell loss depend on:

• the type of force involved,
• how intense the force applied to the spinal cord is, and
• how long that force persists.

Milder spinal cord injury may cause incoordination and a “drunken sailor” style gait. More advanced injury can progress to loss of the ability to walk or an inability to move the legs voluntarily. In the most severe cases, there can be complete loss of pain sensation, which often indicates a poor likelihood of recovery, depending on how long pain perception has been absent.

Chondrodystrophoid dog breeds (e.g., Dachshund, Pekingese, Beagle, Lhasa Apso, and others) represent the overwhelming majority of disc ruptures, with Dachshunds accounting for approximately 45–70% of cases. In these breeds, the typical onset of clinical signs is 3–6 years of age, although spinal radiographs may show disc calcification as early as 2 years. Nonchondrodystrophoid breeds (e.g., Labrador Retrievers, German Shepherd Dogs, and others) most commonly present between 5 and 12 years of age. Ruptures occur most often in the thoracolumbar region (back), representing about 65% of cases, while the cervical region (neck) accounts for up to 18% of presenting cases.

Disc rupture can produce variable degrees of pain. When neurologic injury begins and progresses, clinical signs typically develop in a consistent sequence:

• Back or neck pain, sometimes with reluctance to walk around the room.
• A wobbly, “drunken sailor” gait or hind-end weakness; the hind feet may cross as the pet steps.
• Complete loss of hind limb motor function. Often at the same time, the pet loses the ability to urinate normally and cannot fully empty the bladder.
• Loss of pain perception, indicating severe spinal cord injury and carrying a guarded to poor prognosis.

Disc ruptures are commonly categorized by broad anatomic regions, including:

• 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 regional classification is referred to as neurolocalization, and it helps an ACVS board-certified surgeon decide which diagnostic tests and possible surgical options are most appropriate. Intervertebral disc rupture is generally considered a true surgical emergency, and prognosis varies greatly based on how much neurologic function remains at the time the pet is examined and treated surgically.

Figure 1. Lateral myelogram of a Dachshund with a herniated disc.

Many primary care veterinarians will recommend baseline health screening along with one or more of the following imaging approaches:

• Blood tests: complete blood count (CBC), serum chemistry panel, and urinalysis
• Radiographs of the spine or chest
• Myelogram: a series of radiographs obtained after injecting contrast dye around the spinal cord to reveal areas of compression (Figure 1)
• CT scan instead of, or following, a myelogram
• MRI in addition to, or as an alternative to, CT
• Spinal tap performed at the same time as imaging

Your veterinary surgeon will select the most suitable diagnostic plan, which can differ between patients.

Figure 2. Intraoperative photograph of the patient from Figure 1. Part of the bone over the spinal canal has been removed (hemilaminectomy) to expose the spinal cord and remove the herniated disc material.

Non-surgical management—typically involving strict confinement/cage rest and pain control—is most commonly offered only when this is a first episode of recent onset and neurologic deficits are mild. Further discussion with your veterinarian may lead to referral to a veterinary surgeon to fully review available options.

There are numerous surgical techniques and approaches, which vary depending on the surgeon and the disc location. The specific operation chosen is determined by the veterinary surgeon based on experience and preference. Surgical decompression of the spinal cord, most often achieved by removing bone over the spinal canal, is almost always recommended (Figure 2).

Most pets go home 3–7 days after surgery and typically return for follow-up and removal of skin sutures or staples (if used). Postoperative pain is usually well managed with medications administered by the owner.

Postoperative recovery plans may include:

• Bladder expression 3–4 times per day (if needed)
• Physical rehabilitation to rebuild strength and improve flexibility
• Strict exercise restriction (“bed rest”) for at least 4 weeks
• Lifestyle adjustments, such as weight reduction, using a body harness rather than a neck leash, and limiting jumping off furniture

Potential postoperative complications include:

• Seizures within the first 24 hours after a myelogram
• Infection of the surgical incision
• Future disc herniation later in life (approximately 25% recurrence)
• Persistent wobbliness or dragging of the hind toes during walking

Outcome depends strongly on injury severity and location. In dogs that retain pain perception, surgery can allow about 90% to regain limb use, although some may continue to have mild gait instability. With strict medical management alone, about 60–80% of these dogs may regain function. In contrast, in pets with complete loss of pain perception, surgery may allow 50–60% to recover limb use, whereas strict medical management results in less than 10% regaining function. Overall recovery from intervertebral disc disease is often prolonged, typically taking weeks to months. Recovery with medical management alone generally takes substantially longer than recovery after surgery.

Pets that lose hindlimb function may also be unable to urinate effectively. If neurologic function improves, the ability to urinate independently may return. Until then, owners must manually express the bladder several times daily to empty urine. These dogs have increased risk of chronic urinary tract infections and urine scalding. Additionally, without motor ability, patients cannot reposition themselves and may develop pressure sores and wounds. Providing a soft, well-padded resting area can reduce or prevent these injuries. Some patients may also experience abnormal tingling sensations (paresthesia), which may gradually resolve or persist and lead to self-trauma.