Thoracolumbar Intervertebral Disc Disease

Thoracolumbar Interveterbral Disc Disease

Provided courtesy of:
Michael Wolf, DVM; Diplomate ACVIM (Neurology)

Specialist in Neurology and Neurosurgery
at the Oakland Veterinary Referral Services, P.C.
1940 S. Telegraph Rd.
Bloomfield Hills, MI 48302
OVRS

Intervertebral Disc Disease

Intervertebral disc disease (IVDD) is one of the most common neurologic syndromes seen in dogs. Disc degeneration occurs in almost any breed, but small breed dogs are overrepresented with the condition (Dachshunds, Beagles, Basset Hounds, Pekingese, Cocker Spaniels, Poodles, etc.). The aging process of the disc (degeneration) in these breeds leads to mineralization (calcification) of the disc early in life, which predisposes them to "rupture" a disc. The thoracolumbar spine (back) is the location of a disc rupture in about 80% and the cervical spine (or neck) in about 20% of the patients seen. This paper will concentrate on the more common thoracolumbar intervertebral disc disease.

Anatomy of the Disc

Intervertebral discs act as elastic cushions between the vertebral bodies and extend from the neck region to the tail. They absorb shock and facilitate movement of the vertebral column. The intervertebral disc consists of two portions: an outer ring or annulus fibrosis spinal cord

made up of firm fibrous tissue and an inner part, the nucleus pulposus, which is filled with jelly-like material. When the disc degenerates it loses its elasticity when the jelly-like center calcifies and takes on a gritty, hardened consistency. The disc is no longer able to act as a cushion between the vertebrae and the center part of the disc is predisposed to bulge and rupture through the outer ring into the spinal canal resulting in pain, compression of the spinal cord, and neurological deficits (paralysis).

Clinical Signs

Clinical signs depend on how much, how fast, and with what velocity the disc material has compressed the spinal cord. A mild rupture may cause "just" back pain, while a more moderate rupture causes a wobbly gait and weakness to the hindlegs. If a large amount of disc material ruptures, or if it ruptures very quickly and enters the spinal canal with high velocity, it will cause severe compression and swelling of the spinal cord. These events can spine

lead to complete paralysis of the hindlegs and sometimes even life threatening bleeding inside the spinal cord. There is a very important anatomical difference between dogs and humans. In dogs the spinal cord extends all the way down to the pelvis. In humans the spinal cord ends in the middle of the back and the spinal canal contains then "only" nerves rather than spinal cord. This is the reason why disc disease in humans usually leads "only" to a "pinched nerve." In small breed dogs however, a disc rupture will, with very few exceptions, always lead to compression of the spinal cord. This anatomical difference is so important because the spinal cord is a much more delicate organ than a nerve and is much more susceptible to potential permanent injury.

In addition to various degrees of weakness to the hindlegs, dogs that cannot walk also suffer from impaired urinary bladder control. In these cases, the bladder must be manually emptied to prevent retention of urine and bladder infections.

Diagnosis

A presumptive diagnosis of IVDD is based on the dog's breed, age, history, and neurological examination. Radiographs (x-rays) can show the presence of degenerative, calcified discs. However there can be multiple degenerative discs and calcification does not indicate actual disc rupture. A definitive diagnosis therefore always requires a special radiographic procedure. A myelogram involves injection of a contrast material around the spinal cord to document the exact site of the ruptured disc material, location of compression, and swelling of the spinal cord. Exact localization of the ruptured disc material through myelography is imperative for surgical treatments.

Treatment and Prognosis

There re basically two treatment options for a dog suffering from disc disease. Conservative treatment consists of strict immobilization (cage rest) and sometimes additional medical treatment for inflammation and pain (corticosteriods). Surgical treatment provides decompression of the spinal cord. The ruptured disc material is actually removed from the spinal canal. Dogs experiencing their first episode of back pain with no neurological deficits may be treated conservatively. Recurrence of back pain, however, occurs frequently and a patient with recurrent painful episodes should therefore be treated surgically. (80% of these dogs have spinal cord compression!) Dogs with significant neurological deficits (weakness to the hindlegs or inability to walk) are not good candidates for conservative treatment. Without surgery, neurological improvement is frequently delayed and often incomplete. Furthermore these patients suffer from significant pain during confinement. Moreover, there is a risk of sudden neurological deterioration resulting in complete paralysis and possible irreversible spinal cord damage. Therefore these dogs should be treated by surgical decompression. By removing the slipped disc material the surgical procedure (hemilaminectomy) provides immediate pain relief and also provides the conditions needed for fast and complete neurological improvement. There is also a much smaller chance for recurrence of clinical signs with surgery in comparison to conservative treatment. The success rate for these patients treated by decompressive surgery is over 95%. Finally, dogs which are completely paralyzed and have lost all their feeling to the hindlegs (deep pain) only have a chance to recover when treated with decompressive surgery. Removal of disc material within the first 48 hours after onset of paralysis can still have a success rate of 50%. However, left without surgery, or if surgery is delayed, 99% of these patients stay permanently paralyzed.

The overall prognosis depends on many factors:

severity of neurological dysfunction
the length of time the disc has ruptured and is compressing the spinal cord
the degree of spinal cord swelling
how quickly the disc ruptured (minutes to over several days)
the amount of disc material that has ruptured
the number of previous episodes of back pain
the overall physical condition of the patient

Post Operative Care

A very important part of post surgical treatment is nursing care. Generally patients are confined to a cage or small area for two weeks after surgery. Nursing care consists of manual urinary bladder expression if needed, providing soft and clean bedding, and keeping the patient clean and dry to prevent urine scalding and pressure sores. Recovery can take anywhere from a few weeks to several months. Dogs which can still feel their hindlegs prior to surgery usually can walk or start walking two weeks after surgery. For dogs without deep pain the recovery time is significantly longer and can take up to several months. For some dogs which stay permanently paralyzed, a cart may be an option to provide them with a better quality of life. The cart is a wheelchair of sorts for dogs that allows the back legs to sit in a sling and is propelled by the front legs.

Physical therapy is particularly helpful to maintain joint flexibility and blood circulation to the hindlegs in patients with longer recovery periods after surgery. Physical therapy should be started as soon as the patient can tolerate it. Range of motion exercises, tailwalking, swimming, and whirlpool baths are excellent physical therapy.