Ankylosing Spondylitis Diagnosis and Tests
Diagnosis of AS: (including investigations):
Clinical evaluation, detailed case history, physical examination supported by laboratory investigations will help conclude the diagnosis of AS.
The examination can demonstrate signs of inflammation and decreased range of motion of the joints. This can be particularly apparent in the spine. The flexibility of the low back and/or neck can be decreased. There may be tenderness of the sacroiliac joints of the upper buttocks. The expansion of the chest with full breathing can be limited because of the rigidity of the chest wall. Severely affected people can have a stooped posture.
Inflammation of the eyes can be evaluated by the doctor with an ophthalmoscope. Further clues to the diagnosis are suggested by x-ray abnormalities of the spine and the presence of the blood test genetic marker, the HLA-B27 gene. Other blood tests may provide evidence of inflammation in the body. For example, a blood test called the sedimentation rate is a nonspecific marker of inflammation throughout the body and is often elevated in conditions such as Ankylosing spondylitis.
Urine Analysis is often done to look for accompanying abnormalities of the kidney as well as to exclude kidney conditions that may produce back pain that mimics Ankylosing spondylitis.
Investigations:
Most routine investigations are:
- X-Ray of the lumbosacral spine
- HLA-B27 (blood test)
- MRI spine
- RA test (blood), ANA test (blood) to rule out Rheumatoid Arthritis
- Routine blood test (CBE, ESR)
Other investigations may include, depending on the case:
- Low-grade anemia of chronic disease may be present.
- Antinuclear antibody (ANA) and rheumatoid factor (RF) are within reference ranges.
- Erythrocyte sedimentation rate (ESR) is normal or mildly elevated; it is more likely to be elevated with active inflammation.
- C-reactive protein may be elevated with increased disease activity but is not a better indicator of inflammation than ESR.
- Serum alkaline phosphatase may be elevated when active bone remodeling is occurring.
- The HLA-B27 antigen is positive 90-95% of the time but, notably, is not always present. Furthermore, its presence is not sufficient to make the diagnosis. The test is most helpful when the diagnosis is not clear.
- Cerebrospinal fluid (CSF) protein may be elevated mildly during acute exacerbations.
Imaging Studies
- Plain radiography of the pelvis shows sacroiliitis or fusion of sacroiliac joints.
- Lumbar spine radiographs may show ossification of the anterior longitudinal ligament and fusion of facet joints. The appearance gives rise to the term bamboo spine. With an extensive fusion of the spine, a patient may have a poker spine.
- CT scan will show bony fusions and eroded laminae and spinous processes.
- MRI may be needed to document atlantoaxial subluxation. MRI may be indicated after trauma to evaluate the spinal cord and to rule out cauda equina syndrome or epidural hematoma.
- Cauda equina syndrome may be inflammatory or compressive.
- In inflammatory cauda equina syndrome, the spinal canal is normal to large with CSF diverticula that are best seen on MRI.
- Plain films or CT scans of the spine may be indicated after trauma to evaluate for bony injury.
Other related diseases (which need to be ruled out):
Patients are also simultaneously evaluated for symptoms and signs of other related spondyloarthropathies, such as psoriasis, venereal disease or dysentery (reactive arthritis or Reiter's disease), and inflammatory bowel disease (ulcerative colitis or Crohn's disease).
Written & Approved by-
Dr. Rajesh Shah
M.D. (Hom.)