Pet Talk | Disc degeneration

 

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By HANNA NETISINGHA

University of Illinois College of Veterinary Medicine

The backbone, or spine, is a complex and amazing structure that is literally central to the well-being and function of vertebrate animals. Made up of a series of squat round bones called vertebrae, the spine protects the nerves in the spinal cord, which transmit impulses between the brain and the rest of the body. It also supports the weight and movement of the body.

When something goes wrong with the spine, the result is pain or even immobility. Dr. Kari Foss, a veterinary neurologist at the University of Illinois Veterinary Teaching Hospital in Urbana, sees dogs every day that suffer from intervertebral disc disease, or IVDD.

IVDD occurs when the disc that sits between two vertebrae to cushion or absorb movement in the spine deteriorates and presses on the spinal cord.

The intervertebral disc is often likened to a jelly doughnut. It has an outer part, called the annulus fibrosus, made up of strong fibers that connect the vertebrae, and an inner part, called the nucleus pulposus, which is gel-filled and acts as a shock absorber. These structures can undergo changes that will cause intervertebral disc disease.

Types of IVDD

"There are two types of intervertebral disc disease," Foss said. "Type I is characterized by the extrusion of the disc. Dogs that have a long back and short legs are more at risk for this type of IVDD. Type II, which is characterized by the protrusion of the disc, is more common in larger breeds of dogs. However, both types of IVDD result in the compression of the spinal cord and can occur in any dog."

Type I IVDD is very common, especially among dachshunds, French bulldogs, beagles and Shih Tzus.

"Type I IVDD occurs when the jelly-like nucleus of the disc extrudes through the fibrous outer layer of the disc and presses on the spinal cord," Foss said. "Over time, the nucleus degenerates and hardens. As a result, it can no longer function as a shock absorber."

In Type II IVDD, the fibrous outer layer starts to break down. Both the outer and inner parts of the disc bulge out and compress the spinal cord.

Diagnosis

Pets with intervertebral disc disease may show a wide variety of clinical signs.

"Pets may present with just neck or back pain, or the signs may be as severe as the pet becoming unable to walk to even losing feeling in its legs," Foss said. "The signs vary based on which disc along the spine is affected and the severity of the spinal cord injury."

No matter the severity of the signs, the diagnostic process will be the same: The first step is a neurologic examination by a veterinarian. Your veterinarian may perform a radiograph (X-ray) of the spine to look for other causes such as a disc infection or bony tumors. However, according to Foss, radiographs confirm IVDD only 60 percent of the time. Therefore, the preferred imaging techniques for this disease are magnetic resonance imaging (MRI) or computed tomography (CT).

Treatment

Treatment for IVDD depends on the severity of disease. "We can offer medical management or surgery if necessary in these patients," Foss said.

Medical management consists of very strict movement restrictions for four weeks, combined with medication and is often recommended for dogs with a first episode of back pain or mild signs.

"Basically the patient is on full cage rest and only taken outside, on a leash, for elimination purposes," Foss said.

Oral anti-inflammatory medications are prescribed for pain control. (Patients that become stressed by being confined to a cage may also need anti-anxiety medications.) The goal of the activity restriction is allow the intervertebral disc time to heal.

Surgical treatment is usually recommended only for patients that are unable to walk, or in dogs with recurrent or persistent back pain. Surgery consists of decompressing the spinal cord by removing the herniated disc material. After surgery, the patient must be confined to cage rest for four to six weeks to prevent additional injury.

Prognosis

According to Foss, "The prognosis for dogs with IVDD depends on several factors, including the severity of the clinical signs, the severity and location of the spinal cord compression and how quickly the signs came on." Prognosis is often discussed on a case-by-case basis.

Generally, the prognosis with surgery in dogs is good for those patients that can still feel their feet; many have an excellent chance to return to walking. Dogs that are managed medically vary with their recovery; if they have minimal to no neurologic deficits and well-controlled pain, they have a fair to good prognosis with medical management.

Dogs that become paralyzed and have also lost pain sensation (ability to feel their feet) are considered an emergency, and the chances for the ability to walk again are very low, even with surgery.

Prevention

Unfortunately, intervertebral disc disease can happen at any time and may or may not be related to activity such as running or jumping.

"Disc degeneration is an age-related process, but Type I disc disease can start as early as 2 years of age," Foss said. "We really can't prevent degeneration of a intervertebral disc, but we try to discourage pets at risk from jumping on and off furniture and engaging in any other high-impact activities."

An archive of pet columns from the UI College of Veterinary Medicine is available at vetmed.illinois.edu/petcolumns/. Requests for reprints of this article may be directed to Chris Beuoy at beuoy@illinois.edu.