A disc is a cushion of cartilage that sits between the vertebrae and acts as a shock absorber. It is composed of a rim of tough, fibrous connective tissue that surrounds a gel-like center called the nucleus. When a disc ruptures, one of two things may happen. The first is that the fibrous capsule breaks, allowing the inner nucleus to push out through the opening and impinge on the spinal cord or a nerve root. This type of rupture is called a Hansen Type 1. The second is that the entire disc, surrounded by an unbroken capsule, can bulge outward. This is called a Hansen Type 2.
The diagnosis of ruptured disc is made by neurological examination and imaging studies including spine X-rays, a myelogram, and possibly a CT scan or MRI.
Ruptured discs in the back of the Hansen Type 1 occur in small breeds such as the Dachshund, Beagle, Cocker Spaniel, Pekingese, and small mixed breeds. In fact, ruptured discs are more frequent in Dachshunds than in all other breeds combined.
The capsule begins to degenerate at about 2 to 9 months of age, and signs of impingement on the spinal cord appear at 3 to 6 years of age. About 80 percent of Type 1 ruptured discs occur in the lower back between the last thoracic and the first two lumbar vertebrae. Most of the remainder occur in the neck. There is often a history of mild trauma, such as jumping off a sofa, but normal movements are sufficient to cause a Type 1 rupture. Occasionally, more than one disc becomes ruptured.
The symptoms of a Type 1 rupture usually come on gradually but can appear with sudden explosiveness. The main sign is pain. The dog holds her back stiffly and may cry or whine when patted or handled in the injured area. She usually refuses to walk up stairs or jump into a car. Neurological signs include weakness, lameness, and a wobbly gait. A dog experiencing the severe back pain of an acute rupture will have a hunched-up position and a tight abdomen. The dog may pant and tremble. Sudden disc ruptures can produce complete hindquarter paralysis.
Hansen Type 2 discs ruptures occur in the larger breeds, including German Shepherd Dogs and Labrador Retrievers. The entire disc, surrounded by its capsule, gradually impinges on the spinal canal. Symptoms appear in dogs 5 to 12 years of age. Because the process is gradual, symptoms progress slowly.
Ruptured discs in the neck of the Hansen Type 1 cause a dog to carry her head low and rigidly, making the neck look shorter. This type of injury is extremely painful. A dog will often cry out when patted on the head and refuse to lower her head to eat and drink. Weakness and lameness involve the front legs. Complete paralysis of all four legs does occur but is rare.
Hansen Type 2 neck discs occur with the wobbler syndrome discussed on page 379.
Treatment: A dog with a sudden onset of symptoms of paralysis requires immediate veterinary evaluation. If surgery is indicated, the best outcome is when it is performed within 24 hours.
Most disc problems involving pain or mild paresis improve with rest and medication. The dog should be closely confined for two to four weeks to allow the disc to return to its former position. Corticosteroids reduce swelling and inflammation. Analgesics relieve pain.
Dogs with neck disc problems should be walked with a chest harness rather than a collar.
Disc injuries that cause paralysis require special handling and transporting, as described for Spinal Cord Injuries, page 375. The most common surgery is called a laminectomy. It involves opening the spinal column and removing the extruded disc material. Dogs undergoing surgery will still need a period of careful rehabilitation afterward.
A newer method is to use of proteolytic enzymes to dissolve the disc material. This is called chemonucleolysis. This may only be appropriate for dogs who are in pain without neurologic deficits. If there are neuological signs, surgery is often the better option because it relieves pressure on the spinal cord more quickly.
Acupuncture and physical therapy may be incorporated into treatment protocols.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.