Intervertebral Disc Disease in Dogs (IVDD)
For centuries, man has bred dogs for specific tasks such as hunting and herding. The friendly Dachshund was bred to eliminate vermin from underground burrows. Its long back and short legs made it perfect for such a job, but also made this breed predisposed to back disease, in particular Intervertebral Disc Disease (IVDD). Dachshunds do not hold this title alone, since breeds such as the Shih Tzu, Basset Hound, Pekingese, Beagle, and American Cocker Spaniel are also commonly affected. Even large-breed dogs like the German Shepherd and Labrador Retriever can develop severe IVDD and require treatment. Although IVDD is most commonly seen in the previously mentioned breeds, it should not be excluded as a potential cause of back pain or neurological dysfunction in other breeds.
What Is IVDD and Why Does It Occur?
Most are well aware of the basic skeletal anatomy of the spine, which does not differ significantly between species. Dogs have 7 neck (cervical) vertebrae, 13 chest (thoracic) vertebrae, 7 lower back (lumbar) vertebrae, 3 fused sacral vertebrae, and several tail vertebrae (depending upon breed and docking practices). The bony vertebrae are separated from neighboring vertebrae by thick, pliable, shock-absorbing discs. These discs are made of two components, a strong, thick outer layer called the annulus fibrosus, and a central portion that is soft and jelly-like, known as the nucleus pulposus. These structures are covered on either end by tough caps of cartilage that attach each disc to the vertebral bones. The vertebrae are further joined by ligaments running above (dorsal) and below (ventral) to the discs. These longitudinal ligaments contain a nerve supply that registers sensations of pain if they are disrupted or inflamed.
In an ideal world, all anatomical structures would maintain flexibility and elasticity throughout the lifetime of the animal. In reality, this is not the case. Intervertebral discs can experience two significant changes that affect their function and lead to disease:
- The inner core (nucleus pulposus) can become dehydrated and mineralized, predisposing it to herniation.
- The annulus fibrosus can slowly weaken over time, allowing it to bulge inward into the spinal canal, compressing the cord.
Hansen Types I and II Disc Disease
Short-legged (chondrodysplastic) breeds can begin to experience degeneration and mineralization of the inner portion of the disc as early as 2 months to 24 months of age. This degenerative process and mineralization often occurs rapidly in young dogs. Dehydration and mineralization of the nucleus pulposus makes it susceptible to violent extrusion (herniation) from the center of the disc through tears in the annulus into the spinal canal, resulting in acute, severe damage to the spinal cord. This type of disc herniation is known as Hansen Type I disc disease. Chondrodysplastic (short-legged and long-backed) dogs, specifically the Miniature Dachshund, are genetically predisposed to this disease. The risk of severe injury to the cord is high in this type of herniation.
Hansen Type II disc disease commonly occurs in older large-breed dogs, such as German Shepherds and Labrador Retrievers. Type II disc disease is characterized by a slow onset of clinical signs in affected animals. The affected disc gradually bulges into the spinal canal, compressing the cord and spinal nerve roots, leading to weakness. These animals may present with acute pain if the bulge worsens suddenly.
Clinical Signs of Disease
Clinical signs vary depending upon the type of disc disease. Dogs with Type I disc disease are usually young (3-4 years), short-legged breeds like Dachshunds and Basset Hounds. These dogs usually present acutely with neck or back pain of varying severity. Neurological dysfunction varies according to severity of cord damage.
Dogs display neck pain by walking with a hunched neck, refusing to lift their head, or refusing to bend their neck from side to side. Petting these animals on their head or neck may result in flinching, yelping, or attempts to bite. Dogs display back pain by walking with a hunched appearance, struggling to lie down, walking slowly, and yelping when their abdomen is touched or they are picked up. They may refuse to jump on or off furniture or use the stairs and react negatively to being touched. Pain may vary from mild to severe, intractable pain.
Dogs with Type II disc disease are usually older (8-12 years), large breed dogs, such as the German Shepherd. They present with mild or no back pain and slowly progressive weakness in their limbs. Occasionally, these dogs can present acute pain and exhibit the same symptoms as dogs with Type I disease.
The Five Grades of IVDD
Severity of neurological signs may be grouped into five categories:
Grade 1: Back or neck pain without any loss of function in a pet’s ability to move its limbs
Grade 2: Weakness (paresis) in a pet’s limbs, but maintaining the ability to walk (ambulatory)
Grade 3: Weakness (paresis) in a pet’s limbs with loss of ability to walk (non-ambulatory)
Grade 4: Paralysis of the limbs with intact deep pain perception
Grade 5: Paralysis of the limbs without deep pain perception
Depending upon the severity of herniation and the damage to the spinal cord, dogs with Type I disc disease will present within any of the above grades. Dogs with Type II disc disease usually present at the stage of ambulatory weakness, but can progress or present with paralysis.
In order to determine the extent of your pet’s neurological disease, your veterinarian will perform a complete neurological examination on your dog. Your pet will be assessed for pain, weakness, normal reflexes, ability to place and move their limbs properly (motor function), and awareness of the placement of their limbs (proprioception). Your pet’s ability to feel light touch on the skin and a pinch to the webbing between the toes will be evaluated. Deep pain is the body’s reflexive withdrawal of a limb in response to a pinch between the toes. The inability to feel this pain and react to it indicates severe spinal cord damage. If you suspect your dog has neck or back pain or any of the neurological signs discussed above, medical attention must be sought immediately.
Beyond the Physical Exam: How Is IVDD Diagnosis Confirmed?
Your veterinarian may feel IVDD is highly likely based upon your pet’s clinical signs of pain and neurological dysfunction, age, and breed. However, they will often recommend further tests to confirm their suspicions. Most veterinary practices are equipped with the ability to take radiographs. X-rays of a pet’s back or neck are usually recommended unless the pet is in too much pain. X-rays will help rule out vertebral body fractures, luxations, tumors, or bone infection as possible causes of back or neck pain not related to IVDD.
The mineralization that occurs in discs during Type I IVDD may be visible on plain radiographs. Some caution is warranted in evaluating radiographs, as they fail to localize the actual affected disc space in 60% of cases of IVDD. Why does it matter that we localize the affected disc space? This information is vital in determining which area of the spine to operate on if surgical intervention is necessary. To determine this vital information, advanced diagnostic techniques, such as MRI or CT scan, are recommended. These imaging studies require referral to veterinary specialty centers and are usually not undertaken unless a client has committed to surgical intervention.
Treatment and Prognosis: Surgical vs Medical Management
Several factors come into play when electing the best treatment for a dog with IVDD, the most important of which are severity of neurological disease and economics. Of the five Grades of neurological disease we discussed earlier, all but Grade 5 (paralysis without deep pain) have some chance of recovery with medical management alone. In fact, Grades 1 and 2 have up to a 90% chance of recovery, regardless of whether surgical or medical management is employed. Dogs with Grade 5 disease are unlikely to recover with medical management alone. In these cases, even surgical intervention offers less than a 60% success rate. For any chance of success, surgery must be performed within 24 – 48 hrs of onset of clinical signs.
Surgical intervention involves removing a portion of the vertebrae on the top or bottom of the affected disc space and removal of the herniated nucleus pulposus, which relieves pressure on the spinal cord. For surgery to be successful, the correct disc space must be operated on in order to relieve clinical signs. Therefore, advanced imaging techniques, such as the MRI or CT scan, are essential. These tests are necessary, but add additional expense to an already costly procedure. There is a chance of recurrence of disc herniation, even after surgical intervention. Owners must be aware of this possibility.
The reality of our world today is that sometimes, despite loving our pets unconditionally, we cannot afford to treat them utilizing procedures that will cost thousands of dollars. In these situations, the more cost effective option of medical management becomes the treatment of choice for many pet owners. Economics aside, medical management is often an excellent treatment for dogs with manageable pain and only mild to moderate neurological signs. Medical management includes the use of medications to relieve pain and inflammation, and physical therapy to help strengthen muscles. Commonly-employed medications include NSAIDS (non steroidal anti-inflammatory drugs) or steroids (please note: these two medications are never used simultaneously), gabapentin or opioids for pain, and methocarbamol for muscle relaxation.
There is emerging evidence to support the use of alternative therapies, such as acupuncture and cold laser therapy, to assist in recovery from IVDD. Physical therapy is recommended to help strengthen muscles and aid in promoting circulation. It is often employed immediately after surgical intervention.
Managing a dog with severe neurological disease from IVDD is difficult, but not hopeless. Even dogs that lose their ability to walk and do not improve, despite surgical or medical management, can live fulfilling lives after being taught to use a wheelchair cart. Owners must learn to express their pet’s bladders, as these dogs are also likely to be incontinent. As long as your pet is free of pain and you can make their environment safe and enriching, keeping a pet who does not regain neurological function is a fulfilling option for many pet owners.
IVDD can be a painful and life-altering disease for affected pets. Fortunately, advances in diagnostic imaging have improved our ability to localize surgical intervention to improve successful outcomes. Medical options are abundant and can be a valid and successful means of treating a pet with IVDD, especially when financial limitations eliminate the option of surgical intervention. Early diagnosis is key, however, and the importance of contacting your veterinarian if your pet has back pain or sudden difficulty using their legs cannot be stressed enough.