Ankylosing spondylitis
Ankylosing spondylitis is the headline act in the concert of seronegative negative spondyloarthropathies. The spondyloarthropathies are a group of clinical syndromes that are linked in disease manifestation and genetic susceptibility and aside from ankylosing spondylitis include reactive arteritis (Reiter’s syndrome), psoriatic arthritis, and enteropathic arthritis. All of these diseases have some overlap, and some unfortunate patients have bits from each disease, and are diagnosed with undifferentiated spondyloarthritis.
Ankylosing spondylitis is the most common inflammatory disorder of the axial skeleton, it is seronegative (as all spondyloarthropathies are). It helps to break the words down. Ankylos (Gr - crooked) and Spndylos (Gr - joint of the back) tells us the main manifestation of the diseases, crooked joint of the back, or, more accurately in modern parlance, an arthritis of the sacroiliac joint (with additional potential systemic manifestations).
There is a useful general rule that can be applied for ankylosing spondylitis, it affects 0.2% of the population, affecting 2% of those who are HLA B27 positive, and 20% of those who are HLA B27 positive with an affected family member. It generally affects men more than women and most commonly presents in those between 20-30. In a significant number of cases AS can be found in young people who suffered from juvenile idiopathic arthritis.
The classic manifestation of AS is onset of low back pain that persists for more than 3 months, is accompanied by early-morning stiffness and is improved by exercise but not by rest. Remember, if the pain is worse in the early morning and gets better with movement, think inflammatory, not degenerative. Patients may or may not have systemic features such as fever, anterior uveitis (25%), episcleritis, heart block and valvular abnormalities. Patients may also eventually develop thoracic kyphosis and hyperextention of the neck, leading to a ‘question mark’ psture.
NICE recommends the modified New York criteria is used for diagnosis:
- Clinical criteria
- lower back pain for 3+ months - improved by exercise not relieved by rest
- Limitation of lumbar spine motion in both sagittal and frontal planes
- Limitation of chest expansion relative to normal values for age and sex
- Radiological criteria
- Sacroiliitis on X-ray (note the classic bamboo spine seen on X-ray is a very late and fairly uncommon feature).
Image: “Bamboo spine ankylosing spondylitis” by Stevenfruitsmaak, CC BY-SA 3.0, via Wikimedia Commons.