Intervertebral Disk

Introduction | Causes & Prevention | Symptoms & Signs | Diagnosis & Test | Treatment Options

Intervertebral Disk

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Introduction

Intervertebral disk disease (IVDD) is a syndrome of pain and neurological deficits caused by degeneration and displacement of all or part of the material inside an intervertebral disk (called the "nucleus" of the disk). An intervertebral disk is a pad of fibrocartilage located between adjoining vertebrae, which are the bones that make up the spinal column. Think of these disks as cushions, or shock-absorbers, between the vertebral bones. Intervertebral disks are subject to degeneration, protrusion, extrusion and herniation, in both dogs and in people. When any of these events happen, disk material enters the spinal canal, which compresses the spinal cord and nerve roots and can cause symptoms ranging from pain to complete paralysis. This is called intervertebral disk disease. In people, it is sometimes referred to as a "slipped" or "herniated" disk. IVDD is one of the most common neurological disorders in small companion animals and is reported to affect 2% of the entire domestic dog population.

Causes & Prevention

Causes of IVDD in Dogs
When disks between vertebrae in the cervical (neck) or thoracolumbar (chest and back) areas of the spine degenerate, the inner disk material can protrude or rupture into the spinal canal. This, in turn, can cause localized compression of the spinal cord (called myelopathy) and/or of nerve roots (called radiculopathy) at the site of the disk damage. Two primary forms of IVDD occur in domestic dogs; these are called Hansen Type I and Hansen Type II. Both involve degeneration of intervertebral disks, but the mechanisms of degeneration and the predisposed breeds are different. Hansen Type I IVDD is an acute hernation of the disk that comes on explosively and typically affects chondrodystrophic breeds (those with breed-specific and acceptable hereditary skeletal deformities, such as Dachshunds, Shih-Tzus, Beagles, Pekingese, Poodles, Corgies, Bassett Hounds and dogs with similar characteristics of genetic dwarfism). Hansen Type II IVDD refers to a more gradual, chronic protrusion of disk material that typically affects nonchondrodystrophic breeds, such as German Shepherds, Labrador Retrievers and Doberman Pinschers. Regardless of the type of IVDD, prompt treatment is necessary to prevent progressive neurological damage.

Preventing IVDD in Dogs
Obviously, one important way to prevent traumatic damage to a dog's spinal cord is to manage its athletic enthusiasm. Regular, moderate exercise is good for healthy dogs, and usually for their owners, as well. Uncontrolled leaping and jumping - especially off of high places like decks, tall furniture, ledges, boulders, pick-up truck beds and the like – is not, especially for dogs with degenerative disk disease. Owners of chondrodystrophic breeds should take special care not to let their dogs jump from high places, as their large bodies and comparatively short legs are especially prone to musculoskeletal and spinal injuries. Obesity should be avoided in any dog. Signs of back or neck pain should be taken very seriously. Owners who suspect a spinal cord injury might want to consult with a veterinarian and perhaps with a veterinary neurologist or orthopedic specialist.

Special Notes
Many dogs with IVDD can be managed without surgery, especially if their disease is diagnosed and treated early in its course. Dogs that have lost deep pain sensation or already have become paralyzed from IVDD have a much more guarded prognosis.

Symptoms & Signs

Introduction
Intervertebral disk disease (IVDD) can cause a number of symptoms in domestic dogs, ranging from signs of mild pain to partial or complete paralysis. Most cases fall somewhere in between these two extremes. The signs of IVDD can mimic those of acutely ruptured disks such as from trauma or otherwise, but the causes are very different. IVDD occurs more commonly in certain breeds but can occur in any breed or mix of breeds and in dogs of any age or gender. IVDD can lead to permanent nerve damage, making timely recognition and intervention extremely important.

Symptoms of IVDD
The observable signs of intervertebral disk disease can be quite variable. Owners of affected dogs may notice one or more of the following symptoms, which can be sudden, intermittent or gradual in onset:

Neck pain and stiffness (reluctance to move the neck and head)
Lowered head stance
Back pain and stiffness
Yelping unexpectedly when touched or moving
Abdominal tenderness or tenseness
Arched back (hunched posture, called "thoracolumbar kyphosis")
Sensitivity to touch (possible aggression)
Sensitivity to movement
Impaired, incomplete or inappropriate urination
Lameness
Dragging one or more legs when walking
"Toeing over" or "knuckling over" when walking or standing
Weakness
Stiffness
Stilted gait; tentative gait
Reluctance to rise
Tremors, trembling, shaking
Lack of coordination ("ataxia")
Abnormal reflexes
Collapse
Paralysis in one or more limbs
Owners often notice similar signs after their dog has engaged in strenuous physical activity or experienced acute physical trauma. An acutely ruptured disk can be caused in an otherwise normal dog by jumping off high places, jumping out of a car or off the bed of a pick-up truck, playing a rousing game of fetch or Frisbee or leaping out of an owner's arms, among other activities. A healthy dog can also suffer acute-onset of disk damage when it has been hit by a car, attacked by another animal or experienced some other form of trauma. This type of acute traumatic injury is not the same as IVDD, although the symptoms can be very similar. IVDD involves a degenerative process and does not result merely from sudden trauma, although sudden trauma can cause rupture or herniation of an intervertebral disk in a dog whose disks already are weakened by IVDD.

Dogs At Increased Risk
Intervertebral disk disease occurs primarily in middle-aged chondrodystrophic breeds (3 to 6 years). When it occurs in nonchondrodystrophic breeds, they typically are older (8 to 10 years). "Chondrodystrophy" is a disorder of cartilage formation. "Cartilage" is a specialized, tough, gristly type of connective tissue that essentially provides a model for bone development and growth. In chondodystrophic breeds such as Dachshunds, Bulldogs and Bassett Hounds, chondrodystrophy is seen as characteristic angular limb deformities and abnormally short legs otherwise known as hereditary dwarfism. Other chondrodystrophic breeds include Beagles, Corgis, Cocker Spaniels, Pekingese, Shih-Tzus and Poodles. Nonchondrodystrophic breeds that are commonly affected by IVDD include German Shepherds, Labrador Retrievers and Doberman Pinschers. Obese dogs of predisposed breeds are especially likely to suffer from IVDD.

Diagnosis & Tests

Introduction
Intervertebral disk disease (IVDD) can be difficult to localize and diagnose. Most general veterinarians will consult with (or refer cases to) a veterinary neurologist or a specialized veterinary teaching hospital when spinal cord damage or disease is suspected.

How IVDD is Diagnosed
The first part of almost any diagnostic protocol is a thorough history and a complete physical examination. When spinal injuries are suspected, a complete neurological examination is warranted. In cases of IVDD, the neurological examination will be consistent with a single, focal lesion in the spinal cord and will help the veterinarian localize the site of injury to a particular section of the spine. However, a neurological examination will not confirm whether intervertebral disk disease is the cause of the dog's injury.

Regular blood work (a complete blood count and a serum biochemistry panel) and a urinalysis are not particularly useful if the sole problem is IVDD; the results of these "initial database tests" will be normal in an otherwise healthy dog. Sampling and assessing the cerebrospinal fluid (CSF) by way of a spinal tap can provide more helpful information, as can an electromylogram (EMG). Typically, CSF analysis is most useful to rule out causes other than IVDD, such as cancer, infection or inflammation from another source. Radiographs (x-rays) of the spine are almost always recommended and typically are performed under anesthesia or heavy sedation. Radiographs can reveal abnormalities in the vertebrae and the spaces between them that can help rule out IVDD, such as bone tumors, fractures, discospondylitis or other potential causes of spinal cord damage. Radiographs can also reveal narrowed intervertebral disk spaces that are consistent with, but not diagnostic of, IVDD.

Another form of medical imaging that is indicated for most dogs suspected of having spinal cord damage is called myelography. This involves injecting a contrast medium directly into the spinal canal, waiting a specific period of time to allow that material to move through the cerebrospinal fluid within that canal, and then taking survey radiographs to look for any pressure points from bulging disk material. Disk herniation and spinal cord compression will usually show up with the contrast between the injected dye and the radiographic outline of the vertebral bones. Other advanced imaging procedures that can be highly useful to diagnose IVDD include computed tomography (CT/CAT scan) and magnetic resonance imaging (MRI). Myelography, CT scan and MRI are all advanced diagnostic procedures that are not routinely available at most general veterinary practices. They are, however, available at specialty veterinary clinics and at veterinary teaching hospitals affiliated with veterinary schools.

Special Notes
While the diagnostic process for dogs with neurological spinal injuries can be quite involved and usually requires the involvement of several different veterinary specialists, it is usually worthwhile. The prognosis for dogs with IVDD is generally quite good if treatment is initiated early in the course of the disease.

Treatment Options

Introduction
Signs of back or neck pain in companion animals should be taken seriously and merit immediate veterinary attention. Early diagnosis and treatment can prevent permanent pain and paralysis in many cases. Veterinarians have a number of tools to help them diagnose intervertebral disk disease (IVDD) and localize the lesion to particular areas along the dog's spinal cord. Once the affected disk has been located, the veterinarians can assess their options and come up with an effective treatment plan. The goals of treating IVDD are to reduce or eliminate pressure on the spinal cord, and to alleviate the inflammation caused by that compression, in order to restore the dog to normal pain-free neurological function if at all possible.

Treatment Options
Treatment options range from rest and conservative medical management to surgical intervention. The exact therapeutic protocol will vary depending upon the severity of the disease. In acute cases, pain management and control of inflammation are the first priorities. Corticosteroids or nonsteroidal anti-inflammatory medications (but not both at the same time), muscle relaxants, narcotics or other drugs to alleviate inflammation and pain may be recommended by the attending veterinarian, together with strict cage rest. When given together, glucocorticoids and nonsteroidal anti-inflammatory medications can cause severe gastrointestinal irritation and discomfort, possibly to the point of intestinal rupture. Authorities strongly suggest that these drugs not be administered to the same animal at the same time.

If medical management does not control the dog's pain and other symptoms, or if the results of imaging suggest that surgery is necessary or appropriate, there are several available techniques that the surgeon may consider. These include a procedure called a dorsolateral hemilaminectomy, and another called a cervical ventral cervical slot. These can be done with or without fenestration (surgical perforation) of adjacent disks. Basically, surgery is designed to decompress the spinal cord at the site of the injury and herniation or protrusion of disk material. Another theoretical option is called chemonucleolysis. This involves using laser ablation or injecting enzymes directly into the affected disks. While this procedure has been described in the literature, it is considered controversial.

Whether or not surgery is undertaken, once a dog is stabilized to the point that its pain and neurological signs are well controlled, there are a number of additional management options to consider. Strictly enforced cage confinement for 3-6 weeks is absolutely essential to a dog's successful recovery. Dogs receiving anti-inflammatory or pain medications may act as if their pain has subsided, when in fact the medication is only masking their symptoms. When this happens, many well-meaning owners see what they think is a marked improvement in their dog's physical condition, and they become less conscientious about enforcing strict cage rest. Owners need to be consistent in confining their dogs for the full period recommended by their veterinarian. All dogs recovering from IVDD should be on well-padded beds, and recumbent dogs should be turned regularly (every few hours) to prevent development of pressure sores (decubital ulcers).

Prescription pain and anti-inflammatory medications typically will be reduced gradually over time. If the affected dog is overweight, it probably will be put on a weight-loss program under the supervision of its veterinarian, to reduce unnecessary future stress on the its spine. Owners should monitor their dog's ability to urinate and defecate normally; manual expression of the bladder and/or manual evacuation of the bowel may be necessary during the recovery period. Affected dogs should get minimal exercise while recovering - walking on-leash only, using a harness instead of a neck collar depending upon the veterinarian's recommendation - and should not be permitted to run or jump freely, as such activities can exacerbate spinal damage. Physical therapy (including swimming and other water exercises and passive range of motion exercises) is commonly used as well.

Other techniques that may be appropriate in addition to medical treatment might include massage therapy to stimulate blood flow to the affected area, and reduce overall pain and stress, possible application of acupuncture or acupressure techniques to alleviate pain, use of herbal or other non-regulated supplements or "remedies" and other forms of follow-up supportive care which may help to increase circulation, ease pain, speed healing and otherwise promote wellness, calmness and comfort. Some of these non-traditional adjunct approaches lack controlled studies of their effectiveness and may not have established quality control methods or ways to assess their benefit to dogs with Intervertebral disk disease. Chiropractic manipulation and "adjustment" of dogs with IVDD are highly controversial among veterinary professionals.

Prognosis
The prognosis for dogs with IVDD is generally quite good. Many dogs with intervertebral disk disease are managed well without surgery, especially if their disease is caught and treated early and if owners are consistent and conscientious about strict cage confinement during the entire recovery period. However, the symptoms of IVVD in dogs treated conservatively have a recurrence rate that approaches 50%, especially if they are allowed to jump freely without supervision and if they are obese. Regular physical therapy seems to reduce this recurrence rate. Dogs that have had surgical decompression have a good chance of full functional recovery within 3 to 6 weeks post-operatively. Dogs that have lost deep pain sensation and are unable to move their legs for several days or weeks before surgery have a much more guarded prognosis.

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