Ankylosing Spondylitis Investigations

Investigations:
Most routine investigations are:

An 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 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 radiography 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 scan of the spine may be indicated after trauma to evaluate for bony injury.