Ankylosing
Spondylitis
Diagnosis
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 joints. This can be particularly apparent in the spine. 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 rigidity of the chest
wall. Severely affected people can have a stooped posture.
Inflammation of 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 for 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:
a. X-Ray of lumbosacral spine
b. HLA-B27 (blood test)
c. MRI spine
d. RA test (blood), ANA test (blood) to rule out Rheumatoid Arthritis
e. Routine blood test (CBE, ESR)
Other investigations may include, depending of 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.
• 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 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 radiography may show ossification of the anterior longitudinal
ligament and fusion of facet joints. The appearance gives rise to the term
bamboo spine. With 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.
o Cauda equina syndrome may be inflammatory or compressive.
o 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 scan 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 dysentry
(reactive arthritis or Reiter's disease), and inflammatory bowel disease
(ulcerative colitis or Crohn's disease).
