Intervertebral disc disease

Intervertebral disc disease (IVDD) is a very common spinal disorder of dogs characterized by degeneration of the disc. Other names for this condition include disc herniation, disc extrusion, disc protrusion, “slipped disc,” and many other lay terms. There are 3 types of disc disease. Type I IVDD is more common in chondrodystrophic dogs, in which there is a chondroid metaplasia of the disc with extrusion of the nucleus pulposus through a tear in the annulus fibrosus. Disc degeneration and mineralization are frequently present by two years of age. Type II IVDD is more common in nonchondrodystrophic dogs. In Type II disease disease, there is fibroid degeneration of the disc with protrusion of the annulus fibrosus. Since the dorsal annulus is thinner than the lateral and ventral portions, disc extrusions and protrusions usually occur dorsally. There is only one ligament between the dorsal portion of the disc and the spinal cord. As a result, spinal cord compression typically occurs with both Type I and Type II disc disease. Finally, Type III disc disease (“traumatic disc”) is a non-compressive spinal cord injury that occurs when nucleus pulposus is extruded at high velocity and either enters the spinal cord parenchyma through a rent in the meninges or causes a contusion of the spinal cord, but then dissipates and no longer compresses the spinal cord. See the Fibrocartilaginous Embolism / Traumatic disc herniation page for additional information.

Signalment

IVDD is most common in young to middle-aged chondrodystrophic dogs, but can be seen in older dogs and in all breeds. It is uncommon to rare in dogs less than 1 year of age, so other differential diagnose should be considered in these patients, such as trauma, malformations (e.g., atlantoaxial subluxation), and meningitis. IVDD is uncommon to rare in cats, but tends to be diagnosed more commonly in older cats and has a predilection for the lumbar spine.

Clinical signs

Patients with IVDD can be presented for evaluation of a wide variety of clinical signs, ranging from pain only to paralysis. Type I disc extrusion most commonly has an acute onset of clinical signs, but may become chronic if left untreated or treated medically. Type II disc protrusion is usually chronic in nature, but can become acute if a piece of annulus tears acutely or if nucleus is extruded through the protruding annulus.

Neurological & physical exam

Neurological exam findings reflect lesion location. Discomfort on palpation of the vertebral column is common. See neurolocalization for additional information.

Diagnosis

Rad - L6-7 disk

Lateral spinal radiograph in a cat with caudal lumbar signs showing a narrowed L6-7 disc space and mineralized disc material (arrow) in the vertebral canal at L6-7

Diagnosis of IVDD generally requires advanced imaging.  Complete blood count (CBC), biochemical profile, T4 in older patients, and urinalysis are recommended as a pre-anesthetic screen. Spinal radiographs rarely provide a definitive diagnosis, but may demonstrate radiographic changes suggestive of IVDD or other diseases with similar clinical findings (e.g., discospondylitis, fracture/luxation, vertebral neoplasia).  Radiographic changes suggestive of disc disease include narrowed intervertebral disc space, widening of the intervertebral synovial joint space, smaller than normal intervertebral foramen (smaller “horses head”), or mineralized / radiopaque material in the vertebral canal. Unfortunately, radiographs very often do not provide a definitive diagnosis.

MRI is the preferred imaging modality since it provides the clearest view of the spinal cord and intervertebral discs.  Extramedullary spinal cord compression at the site of disc extrusion/protrusion is most common.  Mineralized disc material will appear hypointense on all imaging sequences. The compressive material may demonstrate mixed intensity if there is hemorrhage from the venous sinus secondary to disc extrusion.

MRI - C2-3 disc herniation

Sagittal T2-weighted MRI demonstrating a C2-3 intervertebral disc herniation

If MRI is unavailable, CT and/or myelography can be performed.  In many cases, CT without myelography can provide the diagnosis in dogs and cats with an acute Type I disc extrusion, especially if the extruded disc material is mineralized.  Myelography followed by CT (called a CT-myelogram) is recommended in patients in which plain CT does not clearly elucidate the cause of the patient’s clinical sing and in patients with chronic or suspected Type II disc disease.

CT-myelogram C5-6 IVDD

CT-myelogram from a dog with a C5-6 intervertebral disc herniation.

Treatment

Medical and surgical treatment options are available.  Patients with only pain or mild to moderate weakness are candidates for medical management. Activity restriction is the most important aspect of medical management because pain medications and anti-inflammatory medications will hopefully help alleviate pain, but, if the patient’s activity is not restricted, clinical signs are more likely to deteriorate.  The use of corticosteroids (prednisone, dexamethasone, etc.) vs. non-steroidal anti-inflammatory drugs (NSAIDs) as a component of medical management is a controversial topic in veterinary neurology.  Physical therapy and acupuncture may be beneficial as well, but large scale studies are lacking.

Author’s opinion: Many neurologists are strongly opposed to the use of corticosteroids. Prospective, placebo-controlled studies demonstrating efficacy of corticosteroids are lacking in the veterinary literature. That being said, in my experience, I have found that many patients with paresis or ataxia treated with a non-steroidal anti-inflammatory drug (NSAID) prior to referral are less likely to respond to the NSAID than to extended medical management with prednisone. One could justifiably argue that the patient improves with the additional activity restriction than with either medication, but, if this were always true, then more patients would appear to “respond” to long-term NSAIDs. I personally use NSAIDs where there is pain only and prednisone when paresis or ataxia are present, assuming there is no medical contraindication (e.g. diabetes mellitus, hyperadrenocorticism) and no obvious historical, clinical, or radiographic changes suggestive of discospondylitis or other infectious disease process.

Author’s opinion: Even more controversial than the prednisone / NSAID controversy, is the use of high-dose methylprednisolone sodium succinate (MPSS, Solu-Medrol) in paraplegic patients. The “Solu-Medrol” protocol is a diverse treatment protocol in which a high dose of methylprednisolone (e.g., 30mg/kg) is given intraveneously followed by variable numbers of repeated doses of 10-15 mg/kg IV or as a CRI. This “protocol” is extrapolated from human spinal cord injury trials that reportedly showed a benefit from MPSS if given within 8 hours of injury. However, critical review of the actual studies suggests limited improvement with MPSS. The definition of recovery is very different between human and veterinary patients. In human patients, the ability to perform basic life functions (e.g., feeding oneself) is considered “recovery,” but our patients need to be able to walk again to be considered recovered by most clients. Additionally, post-hoc statistical manipulation of the data may have skewed the results toward a beneficial response. There are only a few, small-scale retrospective studies in veterinary medicine, which have showed no clear benefit from the use of MPSS.  Several studies have also demonstrated significant side effects of MPSS. Approximately 1/3 of dogs treated with MPSS develop GI side effects and in one small study, 9 of 10 dogs developed severe GI hemorrhage.  There is currently a large-scale, multi-institutitional, placebo-controlled, double-blind study underway that is investigating  post-operative recovery rates in dogs with paraplegia and absent deep pain perception secondary to Type I IVDD that received either MPSS, polyethylene glycol (PEG), or a placebo.  Hopefully, this study will help put to rest whether or not MPSS or PEG should be used in veterinary medicine.

Imaging and surgery are recommended for patients with suspected Type I disc disease in the following circumstances:

  1. Moderate to severe pain that cannot be controlled with pain medications and other measures
  2. Rapidly progressive paresis or ataxia
  3. Nonambulatory patient
  4. Lack of response to medical management within 2 weeks
  5. Recurrent clinical signs

The surgical procedure that is performed depends on lesion and surgeon preference. In the cervical region, ventral slot surgery is most commonly performed because the disc material is usually located in the ventral or ventrolateral vertebral canal. Occasionally, a dorsal laminectomy or hemilaminectomy needs to be  performed if the compressive material is located more laterally or extends around the spinal cord dorsally.  In the thoracic and lumbar regions, hemilaminectomy is most common, but occasionally a dorsal laminectomy is required. If there is bilateral spinal cord compression, some surgeons perform a mini-hemilaminectomy (pediculectomy). This preserves the articular processes/intervertebral synovial joint and maintains vertebral stability.

Postoperative care

Nursing care and physical therapy are critical to recovery. Pain medications should be given until there is no evidence of postoperative pain.  This author typically uses a pain medication CRI (e.g., fentanyl/ketamine/dexdomitor) for 24-48 hours postoperatively. Oral pain medications are also frequently administered. This author typically discharges patients with an NSAID (assuming patient not previously given corticosteroids) and gabapentin +/- tramadol until suture removal. Transdermal fentanyl patches are occasionally used, but efficacy is highly variable between patients.

Bladder management is very important.  Indwelling urinary catheters should be considered in nonambulatory patients. Patients should be kept on thick, soft bedding and turned from side to side every 4 hours and monitored for development of pressure sores.

Prognosis

The prognosis depends on duration of clinical signs, type of disc disease present and severity of clinical signs. For acute Type I disc extrusions with mild to moderate clinical signs, there is a 50-75% chance that the patient will improve enough to not require surgery. Surgical intervention carries an 85-95% chance for recovery if pain sensation remains intact in the affected limbs, regardless of severity of paresis, with an average recovery time of 2-6 weeks. Recovery is defined as return to ambulation without support. The patient’s gait may never be 100% normal due to spinal cord injury secondary to compression. If the patient has no conscious recognition of pain in the limbs, the recovery rate drops to approximately 50% if surgery is performed in first 24 hours and to 5-10% if performed more than 48 hours after loss of pain perception. Type II disc protrusions have a more guarded prognosis even with surgery. There is approximately a 70-75% recovery rate with surgery. Many patients are clinically worse after surgery and may not recover.
 

Further reading

  1. Brisson BA. Intervertebral disc disease. Vet Clin North Am Small Anim Pract 2010;40:829-858
  2. Griffin JF, Levine JM, Kerwin SC. Canine thoracolumbar intervertebral disk disease: Pathophysiology, neurologic examination, and emergency medical therapy. Compend Contin Ed Sm Anim Pract 2009; E1-E13.
  3. Griffin JF, Levine M, Kerwin SC, et al. Canine thoracolumbar intervertebral disk disease: Diagnosis, prognosis, and treatment. Compend Contin Ed Sm Anim Pract 2009;E1-E14.

 

Last updated by NeuroPetVet on August 7, 2016.