| Discussion: |
Ankylosing spondylitis is a chronic inflammatory disorder of unknown cause with widespread musculoskeletal involvement. The most characteristic features are sacroiliitis and spondylitis. Abnormalities occur in joints and at the sites of attachment of ligaments and tendons to bone, with an overwhelming predilection for the axial skeleton. HLA-B27 antigen is present in a very high percentage of patients with ankylosing spondylitis. This disorder is discussed more fully under its specific name.
Patients with enteropathic arthropathies (ulcerative colitis, Crohns disease, Whipples disease) have spinal abnormalities that are identical to those of classic ankylosing spondylitis in addition to intestinal abnormalities. Bone erosion and sclerosis and joint space narrowing and ankylosis are evident. In ulcerative colitis vertebral body erosions with alterations of vertebral shape (squaring) and syndesmophytes are seen. Eventually, a bamboo spine may be noted.
Spondylitis also occurs in psoriatic arthritis and Reiters syndrome. In both disorders paravertebral ossification may be evident, especially in the lower three thoracic and upper three lumbar vertebrae.
Infective spondylitis refers to the coexistence of osteomyelitis and intervertebral disc space infection. The usual location of infection in the vertebra is the vertebral body. A history of recent primary infection, instrumentation or diagnostic or surgical procedure is common. The most frequently encountered pyogenic organism is Staphylococcus aureus, although other agents, such as Brucella, Pseudomonas, Haemophilus, and Streptococcus also may cause infective spondylitis. In brucellar infection, the most common form of musculoskeletal involvement is spondylitis, which usually involves the lumbar spine. An osteophyte resembling a parrot beak may develop on the spine in brucellar spondylitis. A similar picture, with paraspinal masses, is seen in coccidioidomycosis.
Tuberculous spondylitis may result from infection with nonpyogenic Mycobacterium tuberculosis. The first lumbar vertebra is affected most commonly with adjoining vertebrae being affected to a lesser extent in either direction from this level. A predilection for the anterior aspect of the vertebral body is striking. Infection may spread from the initial infectious focus to the adjacent intervertebral discs because of extension beneath the anterior longitudinal ligament or posterior longitudinal ligament, penetration of the subchondral bone plate, or the presence of an intraosseous lesion that weakens the vertebral body to such a degree that it produces a discal displacement. Paraspinal extension to the adjacent ligaments and soft tissues is frequent. Psoas abscesses may develop and undergo calcification.
Radionuclide studies are helpful in establishing the presence of spinal infection at a stage when radiographs are entirely normal. Single photon emission computed tomography (SPECT) is especially valuable in this regard. CT scanning allows definition of the extent of bone and disc destruction and of paravertebral and intraspinal involvement in cases of infective spondylitis.