Ankylosing spondylitis is chronic form of arthritis which most commonly affects the spine. It may also affect other organs such as lungs, eyes and heart valves. Major possible causes of this disorder are positive HLA-B27 maker, family history of ankylosing spondylitis and frequent gastrointestinal infections. Physical examination, medical history of the patient, laboratory investigations and imaging tests are significant for diagnosing ankylosing spondylitis.
General family and medical history of the patient is essential for the diagnosis as this disease can be hereditary. Physical examination may include some tests such as Schober test, Gaenslen test and neurologic evaluation. Various laboratory tests like erythrocyte sedimentation rate (ESR), determination of C-reactive protein (CRP), complete blood count (CBC) and determination of HLA-B27 gene are important for diagnosing ankylosing spondylitis.
Besides these laboratory investigations, imaging tests like x-ray, computerized tomography (CT) and magnetic resonance imaging (MRI) scan contribute a lot in diagnosing ankylosing spondylitis. The radiographers play an important role in diagnosis, detection and follow-up monitoring of patients having ankylosing spondylitis. Typical x-ray findings in ankylosing spondylitis are reliable for proper diagnosis of this disease.
Due to sacroiliitis (inflammation of sacroiliac joints), there may be indistinctness of the joint and development of bony erosions on the sides of joint with bony fusion. It is considered as a hallmark of the disease which can be detected in x-ray findings. Besides this, there may be development of small erosions in the spine which is followed by formation of syndesmophyte. Because of total fusion of vertebral bodies by syndesmophytes, the spine is called as bamboo spine which can be clearly detected in x-ray.
Patients with ankylosing spondylitis can develop fractures at the cervicothoracic and thoracolumbar junctions. These fractures are known as chalk stick fractures which can be seen in x-ray findings. Besides this, pseudoarthritis (abnormal union developed by fibrous tissue within fracture) appears as areas of diskovertebral destruction and adjacent hardening on x-ray film. The involvement of the posterior elements is an important distinguishing imaging feature. In addition to that, enthesopathic changes and involvement of hip joints can be detected in x-ray findings. The lungs are affected by ankylosing spondylitis in the form of lesion changes in the lungs and progressive fibrous degeneration.
CT scan and MRI scan are helpful for diagnosing ankylosing spondylitis if x-ray findings are normal or inconclusive. The advantages of MRI (magnetic resonance imaging) are detection of bone marrow edema, direct visualization of abnormalities in cartilage and clear detection of erosions. Main benefit of MRI scan is that it does not cause possible radiation hazards. MRI may play a significant role in early diagnosis of sacroiliitis. The detection of synovial enhancement in MRI can be co-related with disease activity according to laboratory tests. MRI has been found to be effective in the detection of bone erosions, bone tissue alterations below the cartilage.
MRI is also found to be sensitive for assessment of activity in the early stage of ankylosing spondylitis and may contribute in monitoring the treatment of patients having active ankylosing spondylitis. In case of chronic ankylosing spondylitis, MRI scan helps to detect pseudoarthrosis, spinal canal stenosis (constriction or narrowing) and diverticula related to cauda equina syndrome (severe compression of nerves present at the bottom of the spinal cord).