Ankylosing spondylitis (AS) is a chronic, systemic, inflammatory form of arthritis that preferentially affects the spine leading to limitation of spine movement. The cause of AS is not fully known, but there is a strong genetic predisposition associated with a genetic marker called the human leukocyte antigen (HLA)-B27.
AS usually begins with back pain and stiffness in the late teen years and early adulthood due to inflammation of the sacroiliac joints (the joints that join the spine to the pelvis) and the spine. AS also has a tendency for affecting sites where ligaments attach to bone. When inflammation affects these areas, the condition is called “enthesitis.”
The most common joints outside of the spine and sacroiliac joints to be affected are the hip and shoulder joints. Other joints such as the knee, wrist, ankle, and elbow can also be involved. Some patients may develop eye inflammation termed “acute anterior uveitis”.
Involvement of the heart and lungs, while rare, can be a complication. There may also be an association with psoriasis or inflammatory bowel disease.
Males are affected twice as often as females. Onset of symptoms after age 45 is unusual. Roughly, 15% of patients have disease onset during childhood.
The earliest symptom can be a dull pain in the buttock region. This occurs as a result of sacroiliac joint involvement. Some patients may have radiation of pain down the upper part of the back of the thigh and be misdiagnosed as having sciatica.
The pain at first may be one-sided and intermittent. It may also alternate, first in one buttock and then the other, but the pain, over time, becomes persistent and involves both sides.
The low back area becomes stiff and painful. This may be accompanied by tenderness along the spine and in the sacroiliac joints.
The back symptoms tend to worsen after prolonged periods of rest so that a patient will say their worst times are late at night and early in the morning. The symptoms improve with physical activity or exercise and worsen with rest.
The back symptoms also worsen with exposure to cold or dampness. Some patients have fleeting aches and pains or tender spots that can lead to a misdiagnosis early on of fibromyalgia.
Sometimes, the first symptom can be pain and stiffness in the middle part of the spine (thoracic region) or even the neck. Sometimes chest pain may be more of a symptom than low back pain.
Eye inflammation in the form of anterior uveitis is the most common non-joint feature of AS. This complication occurs in 25%-40% of patients at some time during their disease.
Clinical examination may or may not be helpful in the early course of the disease. The physician should examine the sacroiliac joints and the entire spine, including the neck. Chest expansion (the ability to move the chest with a deep breath) along with range of motion of the hip and shoulder joints should be measured. A search for signs of enthesitis can be helpful in making an early diagnosis of AS. The areas to search for enthesitis include the spinous ligaments, pelvis, front chest wall, bottom of the heels, back of the heels (Achilles tendon), outside of the hips, and the front of the knees just below the kneecap. This area is called the tibial tubercle.
The muscles along the spine may also be tender.
As the disease progresses, the spine becomes stiffer leading to loss of mobility in all directions. Chest movement also becomes more restricted.
Spinal deformities slowly progress and make the spine more rigid. Some patients may develop osteoporosis. If osteoporosis accompanies the rigidity, then a particularly dangerous situation develops because this rigid osteoporotic spine is very susceptible to fracture even after minor trauma.
The diagnosis of AS is based on physical exam and confirmed by imaging procedures. Symptoms, family history, and the joint exam are the most important tools early on.
X-ray evidence of AS may not be evident early in the course of the disease. Patients may need to undergo magnetic resonance imaging (MRI). MRI can detect subtle inflammatory changes in the sacroiliac joints and other areas of enthesitis early on HLA-B27 typing can be helpful in cases where AS is suspected but the diagnosis remains uncertain.
In cases where AS suspected, the HLA-B27 test may allow the presumptive diagnosis of AS to be made.
However, the presence of HLA-B27 should not be used to diagnose AS in the absence of other supporting history and physical exam evidence.
Dr. Muhammad Khan, the world’s foremost expert in AS, has flatly stated that, “HLA-B27 testing is inappropriate in patients with back pain or arthritis in whom neither the history nor the physical examination suggests the presence of AS. A positive result in this clinical situation would still not permit the diagnosis of AS to be made because up to 8% of the general population possesses this gene.”
Laboratory tests measuring inflammation are of limited value. Elevation of erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) occurs in about 70% of patients with active AS. The problem is that there is not a good correlation between the elevation in these blood tests and disease activity.
It may be that the increases in ESR and CRP reflect the presence of active arthritis in joints outside of the spine. Normal ESR or CRP does not exclude the presence of clinically active AS.
Successful treatment of AS requires a combination of non-drug as well as appropriate drug therapies.
Patient education is important and should include a life-long program of regular stretching and range-of-motion exercise. Smokers should be encouraged to stop smoking.
Use of non-steroidal anti-inflammatory drugs (NSAIDs) is often helpful. Traditional disease-modifying antirheumatic drugs (DMARDs), such as methotrexate, leflunomide (Arava), and sulfasalazine (Azulfidine), are not useful for the treatment of disease restricted to the spine. They may be helpful in patients where peripheral joint arthritis or enthesitis is present.
Tumor necrosis factor (TNF) inhibiting agents, etanercept (Enbrel), adalimumab (Humira), and infliximab (Remicade) are very effective in treating AS patients.
MRI studies have shown that TNF-inhibitors are capable of resolving severe inflammation in the spine as well as in peripheral joints. Whether these drugs can prevent structural damage remains to be seen.
As with all forms of arthritis that require immunosuppressive therapy, close supervision of the patient is mandatory.
Surgery may be required for cases of AS that don’t respond to medical therapy. Joint replacement, in the case of peripheral involvement, and corrective spinal surgery may be needed.
Fortunately, today, quicker diagnosis and more aggressive medical intervention have reduced the need for surgical solutions.
One other note of caution… In patients with significant neck involvement and rigidity, intubation for general anesthesia is extremely difficult and dangerous. These patients should notify the anesthesiologist in cases of elective surgery. They should also wear an ID bracelet advising of their condition.