Intervertebral disc disease (IVDD) involves degeneration of the intervertebral discs that often lead to disc herniation resulting in spinal cord or spinal nerve compression. The syndrome can affect all breeds but toy breed dogs such as Dachshunds and Pekingese are more commonly affected. Clinical signs can range from intermittent pain to complete paralysis. Before we get into the details of the disease a brief anatomy review is needed.
The spine is made up of block bones called vertebrae. Dogs have seven cervical (neck), thirteen thoracic (chest), seven lumbar (back), three fused sacral (tail bone) and a variable number of tail vertebrae (Fig. 1).
Each vertebra is made up of a body, the lamina, which houses the spinal cord, and the facets that are partially responsible for the connection from one vertebra to the next (figure 2). Intervertebral discs are situated between canine vertebrae from the second cervical vertebra through some of the tail vertebra. In dogs and cats the IVD sits just beneath or ventral to the spinal canal. The IVD are comprised of a fibrous outer ring call the annulus fibrosis and an inner gel called the nucleus pulposes. The purposes of the IVDs are to act as both connectors and shock absorbers between each vertebra.
In general IVDD manifests by two different pathologic processes. In toy breed dogs the disc may start to degenerate and dehydrate as early as one year of age. As the disc loses its resiliency, the inner nucleus can herniate up and through the annulus fibrosis putting pressure on the spinal cord or nerves. This process often involves a rapid burst of the disc resulting in acute clinical signs. In large breed dogs the pathologic process usually involves a gradual break down and fibrous repair of the annulus fibrosis resulting in gradual disc bulging and insidious or slow onset of clinical signs.