This article was originally printed in the January, 1997, issue of Tufts University School of Veterinary Medicineís Your Dog newsletter.
Backaches are the bane of many peopleís lives. But weíre in good company. As it turns out, our four-legged canine friends are not immune to back pain either. One of the most painful and potentially debilitating causes of back pain in dogs is intervertebral disk disease (IDD). But due to advances in veterinary medicine over the past decade - coupled with increased owner awareness - the majority of dogs with IDD recover at least some normal functioning.
To understand IDD, it helps to envision the canine vertebral column - a hollow tunnel made up of linked, bony segments (vertebrae) that enclose and protect the delicate, gelatinous spinal cord. The spinal cord is the all-important conduit for nerve impulses between all parts of the dogís body and its brain.
Most of the bony segments of the vertebral column are separated by elastic cushions (intervertebral disks), which absorb compressive forces and allow the dog to move comfortably. Dr. Karl Kraus, associate professor of surgery at Tufts University School of Veterinary Medicine, likens a healthy disk to a "jelly doughnut with a rather fibrous outer covering - the annulus fibrosus - and a springy jelly center that absorbs impact - the nucleus pulposus."
Good Dogs, Good Owners, Bad Disks
Seeing their canine pals in obvious distress, some owners blame themselves for having allowed Rover to jump up on furniture or indulge in a weekend Frisbee game. But owners should rest assured that IDD does not directly result from just one such event. Full-blown IDD stems from disk degeneration that occurs invisibly and progressively over time.
When a dog has IDD, the disk material undergoes chemical changes, loses its elasticity, and ultimately herniates (protrudes abnormally). The protruding disk material catches the spinal cord between a "rock" (the vertebrae) and a "hard place" (the ruptured or bulging disk).
In dogs, IDD most often affects the lower thoracic or upper lumbar areas, but it can also occur in the cervical area. IDD occurs less frequently in the upper thoracic area, where rib ligaments cross over the vertebrae and provide extra support.
The signs of IDD vary, depending on the location of the affected disk and the extent of damage to the spinal cord and adjacent nerves. Dogs with moderate spinal-cord damage in the mid- or lower-back region, where IDD most often occurs, may suffer pain, rear-limb weakness, and loss of muscular coordination. Dogs with severe spinal-cord damage may have hind-end paralysis, become insensitive to painful stimuli, and lose bower and/or bladder control.
Veterinarians recognize two classes of IDD. The "lay" owner, however, may find it difficult to distinguish between the two types because both compress the spinal cord. Approximately 80 percent of IDD is Type I - the acute form of the disease most common in small 3- to 6-year-old dogs, particularly dachshunds, beagles, Pekingese, Lhasa apsos, Shih Tzus, miniature poodles, and cocker spaniels. These breeds often develop disk abnormalities during puppyhood, although the signs of IDD usually donít show up until adulthood.
In Type I disease, after years of invisible disk degeneration, the disk material suddenly bursts into the spinal-cord area, severely traumatizing the spinal cord. A dog seems in perfect health when tucked in for the night may be weak - or even paralyzed - the next morning.
Type II IDD is caused by a bulging disk rather than a burst one. But it too stems from slow, progressive disk degeneration, usually beginning later in a dogís life than Type I. Type II IDD is seen most often in large dogs aged 5 years or older.
Because the signs that suggest IDD do not always mean IDD, your veterinarian will carefully examine your dog before arriving at a diagnosis. Taking into account your dogís medical history, age, and breed, your veterinarian will assess its gait, coordination, pain perception, and reflexes. If the dog is paralyzed and insensitive to pain, the veterinarian may use myelography to precisely locate the disk or disks involved - because serious signs such as paralysis indicate the need for surgery.
During a myelogram, the veterinarian anesthetizes the dog and injects a special dye into the space between the membranes that surround the patientís spinal cord. Herniated or severely bulging disks block the dyeís progress. In a radiograph (x-ray), the affected area appears as a narrowing in the dye column. Because of the spinal cordís fragility, though, myelography can be risky. Thatís why veterinarians may forgo this procedure and rely on clinical observations instead when the IDD seems less severe. Veterinarians occasionally use magnetic resonance imaging (MRI) rather than myelography if MRI equipment is available. MRI results are just as useful as myelogram results, and MRI is far less invasive.
The veterinarian may also analyze a sample of spinal fluid to rule out diseases like meningitis (inflammation of the membranes covering the spinal cord, usually caused by viral infection or immune-mediated conditions) and to test for proteins indicating a spinal tumor.
Rest or Surgery?
The prognosis for each case of IDD is different. In general, the more severe the initial signs, the poorer the prognosis. Chances for recovery are usually greater when veterinary intervention is immediate. A delay of even a day or two after the first signs of IDD appear can mean the difference between full recovery and permanent disability.
If your dog is experiencing its first episode of IDD-related back pain and a mild loss of motor skills, your veterinarian may recommend absolute cage rest for 2 to 3 weeks. (That means carrying your dog outside to "do its business.") Your veterinarian may also prescribe corticosteroid medication to reduce inflammation. If Roverís condition improves, he can gradually return to regular activity as long as it doesnít involve vertebrae-stressing motions like jumping or twisting.
If the clinical signs point to severe spinal-cord compression, veterinarians often recommend surgery to remove the invading disk material. Using the myelogram or MRI as a roadmap, the surgeon will remove part of the bony vertebra in the affected area and gently tease out the disk material - a procedure that Dr. Kraus compares to "extracting a piece of spaghetti encased in a rock."
While some research estimates that IDD recurs in only 5 percent of cases treated, dogs that have a string of degenerative disks and have had more than one episode of back pain are at increased risk of IDD recurrence, according to Dr. Kraus. To prevent a series of ruptures (and surgeries), many surgeons recommend preventive removal of the nucleus pulposus from ten of the most vulnerable disks in the thoracic and lumbar regions (disk fenestration).
Whether or not surgery is involved, Rover may still need to spend a week at the animal hospital getting total rest and close monitoring. Beyond that, a dogís prospects for recovery depend largely on how well its owner follows the veterinarianís instructions and on the dogís overall condition. (Not surprisingly, dogs at or close to their optimum weight have an easier time recuperating.)
If your dog is severely disabled, you may have to apply pressure to its abdomen four or five times a day for several days to express urine from its bladder. Otherwise, "urine retention could lead to an infection that could spread from the bladder to the kidneys - with potentially fatal results," notes Dr. Kim Knowles, assistant professor of medicine at Tufts.
If your dog has temporarily lost bowel control, it will inevitably soil its bed or crate. But you must maintain cleanliness in your dogís quarters to prevent skin scalding and infections. If your dog canít move, youíll also have to change its position periodically to prevent pressure sores. And make sure you convalescing palís bed is well-padded.
Owners should also gently massage and manipulate their dogís limbs to help maintain circulation and muscle tone. Veterinarians sometimes recommend hydrotherapy - placing the dog in a whirlpool bath to stimulate circulation and keep the dog clean. "Towel walking" (supporting some of the dogís weight with a towel slung under its abdomen as the dog walks) is also therapeutic. If your dog seems to have "forgotten" how to walk, you may have to place it on its back and gently "bicycle" its limbs to help it relearn the walking motion.
In addition to giving physical aid, an owner should offer emotional support to a dog recovering from IDD. Says Dr. Knowles, "Some dogs become depressed during recovery and need encouragement from their owners."
Sadly, some dogs never regain the use of their hind limbs. But custom-fitted carts are available to support a dogís hindquarters and give it mobility. (Placing a dog in a cart, however, is not a substitute for physical therapy.) And new approaches to help dogs severely impaired by IDD may be on the horizon. For example, the Purdue University School of Veterinary Medicineís Center for Paralysis Research is investigating certain drugs and nerve-transplant procedures that promote nerve regeneration.