Exams and Tests

• The HLA-B27 antigen is found in 90-95% of persons with ankylosing spondylitis. However, its presence is not sufficient to make the diagnosis. The test for HLA-B27 is most helpful when the diagnosis is not clear.

• Cerebrospinal fluid protein level may be mildly elevated during acute exacerbations of AS.



• Low-grade anemia (decreased hemoglobin level) may be present.

• Plain x-ray films of the pelvis may show sacroiliitis or, later, fusion of sacroiliac joints.

• Spinal x-ray films of the lumbar region may show changes in the ligaments and fusion of facet joints (bony prominences on the vertebrae that form joints with similar projections on the upper or lower aspect of adjacent vertebrae). The appearance of this fusion gives rise to the term bamboo spine. With extensive fusion of the spine, a person may have what is called a poker spine.

• Spinal CT scan may show bony fusions and eroded laminae and spinous processes (parts of the vertebrae).

• Spinal MRI may be needed to document atlantoaxial (first two cervical vertebrae) subluxation (dislocation). MRI may be indicated after trauma to evaluate the spinal cord and to rule out cauda equina syndrome or epidural hematoma (space between the wall of the spinal canal and the covering of the spinal cord is filled with blood).

• Cauda equina syndrome may be inflammatory or compressive. This may occur late in the disease course.

• In inflammatory cauda equina syndrome, the spinal canal is normal to large with cerebrospinal fluid diverticulae (outpouching) that are best seen on MRI.

• Plain spinal x-ray films or spinal CT scans may be indicated after trauma to evaluate for bony injury.