Intervertebral Disc Disease
Intervertebral Disc Disease (IVDD) a common neurologic syndrome seen in canines. IVDD has been reported in 84 breeds with particular susceptibility in certain small breeds; generally dogs with 'short legs and long backs' (Dachshund, Basset Hound, Beagle, Lhasa Apso, etc.)
Intervertebral discs act as cushions between the vertebrae and function as the shock absorbers of the spine. A normal disc has two regions: a resilient gelatinous nucleus in the center and an outer fibrous ring that encircles the nucleus. A degenerative disc loses its resiliency when its jelly-like center calcifies and takes on a gritty, hardened consistency. No longer able to cushion the vertebrae, the center is predisposed to bulging and to rupture (extrusion), resulting in pressure on the spinal cord, pain, and paralysis.
Mild disc rupture may cause back pain while a more moderate rupture causes weakness and a wobbly gait. If a large amount ruptures, or if the disc ruptures quickly and causes spinal cord swelling, the pressure can result in a potentially life threatening paralysis.
A diagnosis of IVDD is made on the history and neurologic examination. X-rays can reveal the presence of degenerative, calcified discs and may outline narrowed disc spaces with evidence of extruded/ruptured calcified disc material in the spinal canal. A definitive diagnosis may require a myelogram (a contrast dye study of the spine).
An individualís prognosis depends on many factors:
- The severity of neurologic dysfunction,
- The number of previous episodes of back pain,
- The amount of disc material that has ruptured,
- The degree of accompanying spinal cord swelling,
- How quickly the disc ruptured (minutes to over several days),
- The length of time the disc has been ruptured,
- The overall physical condition of the patient
In general, the ability to experience deep pain in the rear limbs and tail area remains the key prognostic indicator. If paralysis is present, how quickly they went down and how quickly they may have lost deep pain perception are the keys to determining if permanent damage has occurred. Therefore, the neurologic status and x-rays are used to determine the severity of each individualís condition and, subsequently, the best treatment.
Individuals experiencing their first episode of back pain with minimal neurologic dysfunction may be treated medically. The medications include corticosteroids to relieve the cord swelling and analgesics to reduce the pain caused by intense inflammation. Patients with recurring painful episodes or significant neurologic deficits are candidates for a hemilaminectomy. This procedure removes one wall of the vertebrae allowing the surgeon to extract the disc material from the spinal canal without injuring the spinal cord. With pressure removed from around the cord, neurologic function may then begin to return.
A second procedure is then performed to remove the center of the adjacent degenerative discs. This procedure can include up to six intervertebral discs and involves cutting a window in the outer fibrous ring of the discs followed by extraction of the calcified centers (fenestration). This fenestration of the disc centers should prevent recurrence of any disc ruptures, while allowing normal, pain free motion at each disc site. As the resected center of each disc center scars, there is little to no effect on back mobility.