OF THE SPINAL VERTEBRAE
Discospondylitis has been defined as a specific infection of the spinal vertebrae and intervertebral discs. It has been referred to as a form of arthritis of the spine, with narrowing of the involved disc spaces. Technically, it is a form of vertebral osteomyelitis (a bone infection), but it can be differentiated from this general classification by the specific and constant involvement of the intervertebral disc, adjacent vertebral bony endplates, and vertebral bodies (Fig.1).
The most common clinical signs of affected dogs included intense, exquisite spinal pain and neurologic weakness. These deficits or abnormalities include slow, progressive incoordination of the limbs caudal to (behind) the site of the lesion. As the swelling, inflammatory response, bony proliferation, and spinal cord compression increase, the syndrome assumes an exquisitely painful course. Although there does not appear to be any breed predisposition, one report indicates a marked prevalence of the syndrome in large dogs, with the thoracolumbar (mid-back) area accounting for the greatest number of discospondylytic lesions.
The mechanisms of entry for the various infectious agents of discospondylitis are difficult to document, but may be classified as one of the following:
Septicemia is defined as a blood infection with circulating bacterial or fungal organisms. This could be from an abscessed tooth, bladder infection, wound, immune disorder, or debilitating disease. The infectious organisms, now circulating in the bloodstream, find their way to the soft tissues adjacent to the vertebrae. In cases of active infection, small abscesses may develop. Reactive bone spurs appear, involving the vertebral bodies, and subsequently spread to the disc between the two vertebrae. In some cases, the body kills the infection and fuses the vertebrae. However, most affected dogs require treatment, due to the pain and neurologic dysfunction, before there is time for this process to occur (Fig.2).
DISCOSPONDYLITIS SECONDARY TO ADJACENT INFECTION
Foreign bodies (i.e. gunshots and foxtails) are the most common sources of reported cases of discospondylitis which result from adjacent tissue infection. The pathologic process is not unlike that previously described. The extensive soft tissue infection invades the adjacent bony structures and, when in the area of the disc space, results in true discospondylitis.
Treatment of discospondylitis in the dog follows guidelines similar to those used in man. Long-term antibiotic therapy (4 to 6 weeks) is the most common treatment. This treatment is usually aimed at the most commonly isolated micro-organism, Staph. aureus. When no response to therapy is noted or when recurrence is a problem, surgical biopsy, bacteriologic culture, and antibiotic sensitivity testing are needed. When severe neurologic deficits exist they are directly related to pressure on the spinal cord, which must be reversed in some cases. Antibiotics in conjunction with surgery (decompressive laminectomy or hemilaminectomy) and occasional internal spinal immobilization have proven very successful.
Ultimately, spontaneous fusion must be achieved either with antibiotic therapy alone, or in combination with spinal surgery, to maintain immobilization and allow healing by bony consolidation. In most cases, progression of bony healing and joint fusion become evident by radiographic (x-ray) evaluation within a few weeks. This healing will be followed by your veterinarian with periodic evaluations. These evaluations document the subsiding soft tissue reaction as the vertebrae and disc return to a more normal appearance following bony fusion of the involved areas.
1998, Southern California Veterinary Surgical Group