Investigations
1st investigations to order
pelvic x-ray
Test
Pelvic films should be requested in all patients presenting with inflammatory back pain.
Sacroiliitis may be unilateral or bilateral and is graded from 1 to 4 depending on the severity.[100]
The presence of radiographical sacroiliitis is a requirement for fulfilling the modified New York classification criteria for AS, which is the most specific criteria set for reaching a diagnosis.[3][101]
Radiographically apparent sacroiliitis may take many years to develop, and therefore a normal pelvic x-ray does not exclude the diagnosis.
Radiographical severity tends to be lower in women than men.[17][Figure caption and citation for the preceding image starts]: Plain x-ray showing bilateral sacroiliitis in a patient with ASBMJ 2006 Sep 16;333(7568):581-5. © BMJ Publishing Group Ltd 2009 [Citation ends].
Result
sacroiliitis
Investigations to consider
HLA-B27
Test
HLA-B27 is not diagnostic and should not be tested in all patients with back pain. HLA-B27 is present in about 90% of patients who have AS.[18]
In a patient with classic inflammatory back pain and normal radiographs, a positive HLA-B27 in the presence of 1 or 2 associated features of AS should prompt the request of an MRI.
Sensitivity 90% and specificity 90%.[102]
Result
positive or negative
MRI
Test
Instrumental in allowing clinicians to diagnose AS early.
MRI scans may demonstrate abnormality in the presence of normal radiographs.[84][85][103]
It is also useful in the detection of enthesitis (inflammation of the tendon or ligament attachments to bone).[104]
The physician should request a T1 and STIR image. Gadolinium enhancement is not needed.
The MRI may be useful in evaluating response to treatment.
In young patients, early use of an MRI is advocated to avoid excessive radiation from plain radiographs.[Figure caption and citation for the preceding image starts]: Coronal STIR (short tau inversion recovery) magnetic resonance image showing unilateral (right) sacroiliitisBMJ 2006 Sep 16;333(7568):581-5. © BMJ Publishing Group Ltd 2009 [Citation ends].
Result
bone marrow oedema on a T2-weighted sagittal short-tau inversion recovery (STIR) image
cervical spine x-ray (lateral)
Test
Cervical spine films should be requested for all patients with confirmed AS to assess disease at baseline and to assess progression.
The lateral cervical and lumbar films can then be used to calculate the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS), which is a composite score calculated at specialised centres to quantify the degree of structural damage in the spine.[105]
It is important to evaluate these x-rays if the patient gives a history of a fall, to exclude trauma.
A syndesmophyte is an osseous excrescence attached to a ligament.
Bamboo spine in late disease may be demonstrated in a minority of patients.
Result
erosions, squaring, sclerosis, syndesmophytes or bridging syndesmophytes in the cervical spine, bamboo spine (late disease)
lumbar spine x-ray (lateral)
Test
Lumbar spine films should be requested for all patients to assess disease at baseline and to assess progression.
The lateral cervical and lumbar films can then be used to calculate the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS).[105] A syndesmophyte is an osseous excrescence attached to a ligament.
Bamboo spine in late disease may be demonstrated in a minority of patients.[Figure caption and citation for the preceding image starts]: Bamboo spineStudent BMJ 2002;10:303-52. © BMJ Publishing Group Ltd 2008 [Citation ends].
Result
erosions, squaring, sclerosis, syndesmophytes or bridging syndesmophytes in the lumbar spine, bamboo spine (late disease)
thoracic spine x-ray (lateral)
Test
Thoracic spine films should be requested for all patients to assess disease at baseline and to assess progression.
Bamboo spine in late disease may be demonstrated in a minority of patients.[Figure caption and citation for the preceding image starts]: Bamboo spineStudent BMJ 2002;10:303-52. © BMJ Publishing Group Ltd 2008 [Citation ends].
Result
erosions, squaring, sclerosis, syndesmophytes or bridging syndesmophytes in the lumbar spine, bamboo spine (late disease)
ultrasound
Test
An ultrasound may be necessary to confirm and/or quantify the extent of enthesitis (inflammation of the tendon or ligament attachments to bone).
Result
enthesitis
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