Surprisingly common cause of longstanding low back pain.
What is Ankylosing Spondylitis?
It was recently reported in the Australian Family Physician that delay between the onset of symptoms and diagnosis is 5-7 years on average (research was published in 2008). This reflects the difficulties that The GP faces in making an early diagnosis, but there are efforts nowadays to try to make an earlier diagnosis. As with many medical problems, however, early diagnosis may not straightforward because the symptoms, signs and test results may not be conclusive.
Ankylosing Spondylitis (AS) is a reasonably common musculoskeletal problem. It is a chronic inflammatory condition of the axial skeleton (ie. the spine). “Ankylosis” refers to bridging of joints, and “spondylos” is Greek for a spinal vertebra, so the condition refers to bridging of the spinal vertebra caused by fibrous or bony connections between disc spaces.
The condition is 5 times more common in men than women. AS usually starts causing symptoms from the late teens to early 30’s. Approximately 1 in 20 people with low back pain lasting some time have the condition.
Typical symptoms are low back pain with morning stiffness. The back pain usually improves with exercise. Symptoms vary, though, and pain can be felt elsewhere (eg. pelvis, down the legs as sciatica, cervical spine).
Thankfully only a minority of patients develop severe Ankylosing Spondylitis. The condition can sometimes affect large joints and the hip.
So What are the main “clues” to Ankylosing Spondylitis?
The condition may be considered when back pain occurs gradually in younger men, the pain improves with exercise, and/or the back is stiff in the morning on waking (for at least an hour). The condition is more common in people who have had colitis or psoriasis or a history of “iritis’ (eye inflammation, not conjunctivitis), or if there is a family history, but many people diagnosed will not be in these groups – it’s just easier to think of AS in the first place!
More recently recognised specific features of the condition are alternating buttock pain, and A particularly useful (relatively recent) pointer is waking up only in the second half of the night with spinal pain or stiffness. This is important because the traditional pointer is prolonged morning stiffness but it can be difficult for people to know how long their back is stiff after waking (because it’s hard to distinguish pain from stiffness).
Early in the course of AS, it may not be possible to make a firm diagnosis and it may be necessary to review the possible diagnoses again in the near future.
What are the tests?
Examination may show reduced flexion of the lower back (this can be formally measured using the modified schober’s test), and other signs may be positive although often are not.
Blood tests can be a useful pointer but are often not diagnostic. Many patients ask for HLA-B27 and this can indeed be useful but is only one of a range of pointers to the diagnosis and it’s far from being a black-and-white test. For example, only 1 in 20 people who are HLA-B27 positive ever develop AS. On the other hand, a negative HLA-B27 does help rule out the diagnosis (but not completely as 10-15% of patients with AS are HLA-B27 negative). The typical tests for inflammation are a CRP and ESR. These may be normal, however, with AS.
The diagnosis of ankylosing spondylitis is usually confirmed on xrays or other imaging. Xrays are normal early-on so an MRI of the spine & sacro-iliac joints may be required. Indeed, as the whole idea is to diagnose it early, a normal Xray doesn’t really help much and an MRI is generally needed (there are other radiological tests that may be used instead but MRI is the main one).
There are other causes of “inflammatory back pain” other than AS but AS is the archetypical one.
A referral to a Rheumatologist would generally be indicated confirm the diagnosis. In addition, a few people do develop more severe AS and can benefit from specific biological therapies that have newly emerged (or the traditional disease modifying anti inflammatory drugs). The likelihood is, however, that the diagnosis will be confirmed and the patient asked to take over the counter medication (non steroidal anti inflammatory drugs) and exercise / mobilise regularly.
Longer term monitoring checks on the impact symptoms, a physical examination (e.g. modified schober’s test and other clinical tests) and possibly blood and/or imaging tests. This is mainly patient-driven – some people have milder AS, and some need regular GP and/or rheumatological review.