Ankylosing spondylitis (AS) is the main form of sponyloarthritis. AS predominantly affects the axial skeleton (spine and sacroiliac joints). The main symptoms are lower back pain and stiffness. The pain and stiffness are usually worst overnight and first thing in the morning and gradually improve over the course of the day.
The main site of inflammation is where the ligaments in the back insert into bone. Over time, inflammation at this site causes the ligaments to ossify (become bone) and therefore result in the spine fusing. Other joints (e.g. hips or shoulders) and where tendons insert into bone (e.g. the Achilles tendon inserting into the heel) can also become inflamed. Inflammation of the eye (uveitis) and inflammatory bowel symptoms can be part of ankylosing spondylitis. Occasionally the lungs or the aortic valve of the heart can be affected.
A gene called HLA B27 is associated with the risk of developing ankylosing spondylitis. The number of patients in the general population with this gene in New Zealand is approximately 10%, but only 1/20 with the gene will go on to get ankylosing spondylitis. About 10% of patients who develop ankylosing spondylitis do not have the HLA B27 gene so there are obviously other factors that contribute to developing the disease. The HLA B27 gene is also associated with other disorders such as reactive arthritis, iritis, inflammatory bowel disease and psoriatic arthritis. Ankylosing spondylitis is much more common in males than females and the disease tends to be more severe in males. Typical age of onset is in the late teens and early 20’s, and the onset of symptoms after the age of 40 is very rare. The diagnosis is often delayed by several years because back pain is very common and the symptoms are often attributed to minor back injuries or manual work.
The diagnosis of ankylosing spondylitis is usually made by a rheumatologist based on the history of lower back pain and stiffness and examination findings that show tender sacroiliac joints and restricted back movement. Some patients have restricted chest expansion. X-ray’s, CT or MRI scan showing ‘sacroiliitis’ or ankylosis of the spine is usually needed to confirm the diagnosis. A positive gene test for HLA B27 can help with the diagnosis if the imaging in not conclusive.
Disease activity is measured using a tool called the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) – which is a series of 6 questions scored on a visual analogue scale from 0-10cm on back pain, back stiffness, other joint symptoms, local areas of tenderness and fatigue. Limitation in movement is based on the Bath Ankylosing Spondylitis Metrology Index (BASMI) – which measures lumbar spine forward and side flexion, neck rotation and intermalleolar distance. Chest expansion is also usually measured.
Treatment for ankylosing spondylitis is dependent on the severity of symptoms and how restricted certain back movements are. Basic treatment consists of regular anti inflammatories, stretching and strengthening exercises. The exercises are often supervised by physiotherapists – usually for the first 3 months. Where available, hydrotherapy can be useful. Sometimes the sacroiliac joints are injected with cortisone.
If the above treatment options fail, and a patient still has severe ongoing symptoms (based on a high BASDAI score) and they have marked restriction in back movement and/or chest expansion then they may be eligible for a class of medication called anti-TNF therapy. Anti-TNF therapy is usually effective in treating symptoms in most patients with the disorder. In New Zealand, the 3 available anti-TNF's are adalimumab (self-administered skin injection every 2 weeks), etanercept (self-administered skin injection weekly), and infliximab (intravenous infusion 6-8 weekly). All 3 are very expensive and come with certain risks such as increased risk of infection, so are not appropriate for all people. A certain amount of pre-treatment screening for latent infections and extra vaccinations are required. Funded access to anti-TNF therapy is determined by the PHARMAC special authority criteria.