Investigation
Clinical tests
Chest expansion measurement
- measure chest circumference in full expiration and inspiration, Pathological difference < 2 cm is suggestive of AS
Spine mobility tests
Schober’s test
- Two points, one 10 cm above and 5 cm below the lumboscaral junction is marked in upright position and then the patient is asked to fully flex forward and the expansion is noted. It is considered abnormal if the expansion is less than 5 cm
Examination of the hip
Mennell sign
- Tenderness to percussion and pain on displacement of the sacroiliac joints
FABERtest
- FABER (Flexion, Abduction, and External Rotation) provokes pain in the ipsilateral hip
Laboratory findings
- ↑ CRP and ↑ESR
- Auto-antibodies (e.g. RF, ANA) are negative
- HLA-B27 positive in 90 % of cases
X-ray
- Pelvis : Bilateral sacroiliitis, including ankylosis (fusion of the articular surfaces) , Pseudo widening and erosion of sacroiliac joints
- Spine : Loss of lordosis with increasing abnormal straightening of the spine , Sclerosis of the vertebral ligamentous apparatus, Syndesmophytes resulting in a so-called 'bamboo spine' , Signs of spondyloarthritis, including ankylosis of intervertebral joints
- Thorax: Ankylosis of costosternal and costovertebral joints
MRI
- Sacroilitis with high intensity bone marrow oedema
CT
- Sacroilitis , hip arthritis
New York criteria for diagnosis
- Limitation of spine in all plains
- Pain in lumbar spine or dorsolumbar junction
- Chest expansion less than 2.5 cm