Disk Diseases in the Dog

by Christopher Forsythe, DVM

When the phone rang and I heard Sarah talking to the owner about her pet not being able to use his back legs, I had a fairly good idea about what was going on. I started to get that nauseated feeling like I get when I go ahead and eat the foot long meatball marinara at Subway when the six inch would have been enough. Sarah’s advice to get Tango “down to the hospital right away” was good advice, because time was of the essence if we were going to help the little dog. Tango, a very cute little Papillon with the attitude of a much larger dog, had somehow managed to injure his back apparently when he walked through his doggie door, and now had become as uncoordinated as a blindfolded circus-juggler with vertigo. This was the first time anything like this had happened, and Mrs. Karolek was plenty worried.

Clinical signs of disk disease depend on the type of disease and how severely it is causing the spinal cord to be compressed. The findings can range from some mild back pain without any noticeable problem to a pet becoming completely paralyzed in the back legs. If your dog begins walking unsteadily, as if he’s had “tee many martunis,” goes down in the rear and is unable to walk, he may be suffering from intervertebral disk disease, often caused by age-related changes within disks along the backbone which may result in a blown disk.

Thoracolumbar Disk Disease, also known as Hansen’s Disk Disease, describes a set of diseases which cause disk material around the spinal cord to bulge or rupture and impinge on the delicate fibers comprising the spinal cord. This leads to neurological deficits, even paralysis. In other words, dogs can wreck their backs really easily, and the terrible consequences can be devastating.

Two types of Hansen’s Disk Disease are characterized according to whether disk material actually ruptures or simply “bulges” into the canal, but both can cause terrible spinal cord damage. Type 1 Hansen’s (ruptured disk material) occurs frequently in Dachshunds, Shih Tzus, and Pekingese, as well as Welsh Corgis and Beagles and any other “smoosh-faced” or short-boned dogs. Type II Hansen’s (bulging disk) occurs in all large breeds.

This disease is a pain in the @$#%… uh, back!

Pain is a common sign with this disease. The lesion is usually located between segments T3 and L3 in the middle of the backbone. Pain is elicited by careful palpation of the dorsal spinous processes or the “ridge” of the dog’s backbone. Most of the time the diagnosis is not difficult to make. After all, you and your veterinarian will know the pet has back pain, since she will have had trouble walking or be off balance, acting like she is drunk. Some pets present with a hunched up posture and have decreased proprioception in the hind limbs. Proprioception means that when the doctor positions a dog’s foot on its toe and to the side, your pet simply leaves it there, unaware of its abnormal position, instead of placing it back properly as he should. Usually it takes several seconds him to move his foot back underneath, thus indicating there is a delay in the signal between his brain and his foot. Because of the pressure of the bulging disk and the resulting damage to the nerve fibers, he is losing the ability to control his back legs. Unless the problem is isolated properly and corrected soon, he’ll very likely continue to lose nerve function and become weaker and perhaps even experience posterior paralysis.

Once the ability to place the rear limbs is lost, superficial pain sensation begins to disappear, and then eventually deep pain sensation is lost too. Once this happens, the poor dog cannot feel anything whatsoever in the rear legs, and the prognosis becomes much more serious. During this process, the paraprofessional staff play a monumental role, as they so often do in veterinary practice, in relaxing and comforting pets while they are undergoing multiple assessments. As a veterinarian, I cannot say thank you enough to my wonderful staff of veterinary nurses who care for my patients while this process is unfolding.

Once the veterinarian has examined the pet and has initially diagnosed the disk disease, he or she must determine the location of the lesion. It is key that the vet determine whether the pet’s condition is stable and whether the condition should be treated with medicine or surgery.

In either case, getting good quality x-rays of the thoracolumbar spine is important to view the lesion. It is often possible to see a narrowed, wedge-shaped disk space of interest. There may be evidence of mineralized disk material within the spinal canal at the area of the lesion, and the x-ray helps confirm the diagnosis.

If surgery is an option, the doctor may want to run a myelogram test to more closely localize and clarify the lesion. Specialists at a referral center perform this test by injecting contrast medium into the spinal column while the pet is under general anesthesia, then taking detailed x-rays to see the outline of the spinal cord. The veterinary neurologist and surgeon then can visualize the delicate outline of the spinal column and see with clarity the disruption that would confirm and delineate the impingement of the spinal cord causing neurological impairment. This test also helps the surgeon determine exactly where (and if) surgical removal of the material needs to take place.

Medicine or surgery?

Several factors affect the decision whether to take a pet to surgery, including the four categories of patients into which a dog falls: 1) first-time episode of back pain only, (2) repeated episodes of back pain, (3) some degree of paresis (weakness) with deep pain perception left intact, or (4) paralysis and loss of deep pain perception. Medical therapy can be used in category 1 patients only, while surgical therapy is used in categories 1-4.

Medical therapy is delivering steroids within eight hours of pain onset in order to decrease swelling around the spinal cord. The goal is to relieve the pressure on the cord and allow local swelling to diminish until clinical signs wear off and the pet returns to normal. Once the hospital provides medical care and a pet is discharged, owners need to provide good nursing care for their pets and keep them very quiet. We also remind them that relapses are common. Cage confinement and exercise restrictions are paramount for success with a disk patient.

Surgery to remove extruded disk material pressing on the spinal cord can relieve pressure and restore the pet’s normal function. This decompressive back surgery is indicated for category 2-4 patients and is performed at specialty hospitals by highly trained veterinary surgeons. It is directed toward relieving spinal cord compression and can often restore mobility to pets who would otherwise be left permanently paralyzed if left without surgery. Although the surgery is costly and the recovery is slow and potentially painful, it offers a chance for pets for mobility, recovery, and a wonderful quality of life.

Tango, save the last dance for me?

Mrs. Karolek was shaking when she brought him in, and he was uncertain where his rear legs were. I stood him up and he fell to the left. I stood him back up; he plopped down to the right. I curled his left rear paw top-side-down, and he just left it there like it wasn’t even attached. Five seconds later he managed to wrangle it back under himself. Same thing with his back right foot. By testing his reflexes in the back, I found they were on overdrive. Luckily when I pinched his back toes with an instrument he responded with a little bite, thus letting me know it hurt, and that he was not planning to sign up for my fan club anytime soon, though he still thought I tasted OK. He was weak in the rear, but he still had pain sensation, so there was time to assess him.

X-rays and steroids

Tango, the little Papillon with ears as big as sister Betrille from The Flying Nun, remained cooperative as we took digital x-rays of his thoracolumbar spine, which revealed a small lesion between his first and second lumbar vertebrae. The lesion, though small, was noticeable on the x-ray and indicated Hansen’s disk disease, common in small breeds of dogs. Discussing the options, possible outcomes, and prognosis, the owner opted for medical management with IV fluids and steroids with hospitalization and cage rest to see how Tango would respond overnight. I agreed to the owner’s wishes that I manage the case medically that night and assess Tango daily for progress, hoping he would improve gradually and be able to avoid surgery. Mrs. Karolek understood that if the clinical signs of weakness and loss of ability to move and feel pain progressed, Tango would likely need to be transferred to another facility for surgery. Thankfully within 24 hours Tango was already stabilizing and feeling better. As each day progressed, Tango showed improvement and became stronger and in better control of his back legs. After four days in the hospital, little Tango was finally able to stand quietly and eliminate on his own and even take a few small steps without struggling or stammering.

Mrs. Karolek was delighted to bring little Tango home the following week on a tapering dose of steroid and strict exercise restrictions. He has shown marked improvement ever since and continues to amaze all of us at his ability to rebound following his initial ordeal. Follow-up x-rays taken a month later showed the spinal cord lesion to be almost completely resolved and, with careful monitoring, Tango seems to be his old self. Mrs. Karolek is aware that should a relapse occur, surgery would be required, but during this season of hope and healing, she is glad to have her little dancer at her feet, smiling up at her, glad to be around the house. And somewhere around Sonoma, I suspect, there may even be a Flying Nun gracing our presence.