Ankylosing Spondylitis

Among the broad arena of rheumatic diseases, ankylosing spondylitis is one of the forms of inflammatory arthritis characteristically affecting the spine and sacroiliac joint (located at the base of the back, where sacrum, i.e. bone directly above the tail bone, meets iliac bones either side of the upper buttocks). Inflammation in these areas causes pain and stiffness in and around the spine, and over time, chronic inflammation of spine (spondylitis) leads to complete cementing or fusion of vertebrae (ankylosis), thus giving the name ankylosing spondylitis (AS). Other joints of the body like hip, knee, and jaw bones may also be affected, but at lower frequency. It is a systemic disease affecting not only bones and joints, but also other organs like eyes, lungs, heart, and kidneys. It is more severe in males, and is three times more common than in females. It is also one of the leading causes of low back pain in adolescents and young adults, with peak age of onset being 17 to 35 years of age. Presentation after 45 years of age is rare.

What causes it?
Both genetic and environmental factors interplay in the causation of the disease. HLAB27 is the most common predisposing gene found in 90% of the patients with AS. However, HLAB27 gene appears only to increase the tendency of developing the disease, while some additional factor(s), such as environmental, are necessary for the disease to be expressed. For example, seven percent of the population of the United States has HLAB27 gene, but only one percent population actually have ankylosing spondylitis. HLAB27 positive individuals who have relatives with ankylosing spondylitis have six times greater risk of having the disease, compared to those whose relatives don’t have ankylosing spondylitis.

Signs and symptoms
Signs and symptoms can be divided as musculoskeletal and extraskeletal (affecting other part of the body other than bone and muscles).

Musculoskeletal
The disease starts insidiously in young adults with vague initial symptoms. The symptoms are related to inflammation of the spine, joints, and other parts of the body. Typical presentation is low back pain and buttock pain, which is characteristically bilateral and associated with early morning stiffness that improves with exercise and activities, but not at rest. Heat, warm shower, and motion typically improve the symptoms. Within six months to a year, pain and stiffness progressively worsen, with spasm of paraspinal muscles leading to flexors predominance. This results in loss of normal concavity of cervical and lumbar spine, leading to abnormal spinal curvature manifesting as kyphosis (forward bending of spine). As the disease progresses, chronic and severe inflammation of the spine occurs, which results in bony fusion of the vertebrae (ankylosis). Once ankylosis of spine sets in, these patients are particularly at more risk of fractures and dislocation of spine, predominantly cervical spine, when subjected to falls or accidents.

Inflammation of costochondral joints (area where ribs attach to thoracic spines) also leads to chest pain, which might mimic angina, and hence needs to be ruled out. Inflammation and scarring of lungs, along with forward curvature of upper torso, lead to limited expansion capacity of lungs. This leads to patients presenting as shortness of breath and coughing, especially with exercise and infection.

Although peripheral joints are less commonly involved, compared to axial skeleton, patients with AS also have arthritis in joints other than the spine. This feature is more common in women. The patient may have pain, swelling, warmth, and redness in joints such as hip, knee, shoulder, ankle, and toes. As the disease progresses, it may lead to decrease in range of motion in affected joints, with difficulty in walking and change in gait pattern. At this stage, the typical ‘stooped over’ posture becomes evident, in which the patient gazes downward, the entire back is rounded, hips and knees are semiflexed, and the arms cannot be raised beyond a limited amount at shoulder. Enthesitis (inflammation of the insertion points of tendons and ligaments to the bone) manifests in the form of Achilles tendinitis, causing pain and stiffness at the back of the heel, especially while pushing off when walking upstairs. Inflammation of the tissues at the bottom of the foot, causing plantar fasciitis, leading to foot pain and burning sensation, can also be present in some patients.

Extraskeletal
Other areas of the body that are affected by the disease are eyes, heart, and kidneys. Inflammation of iris (colored portion of eye) i.e. iritis, can lead to pain and redness in eyes, especially when looking at bright light. Similarly, inflammation of ciliary body and choroid of the eye (uveitis) can occur, leading to visual disturbance. Scarring of the heart’s electrical system, causing abnormally slow heart rate, may occur in some patients. Inflammation of aortic valves, which causes leakage of blood flow from heart to aorta, leading to cardiac failure, can also be seen in some patients. Advanced spondylitis can lead to deposit of protein material called amyloid to the kidneys, leading to chronic kidney disease and kidney failure.

Diseases that have similar symptoms are:
• Mechanical back pain
• Other seronegative spondyloarthropathies (Reiter’s disease, psoriatic arthritis)
• Degenerative spine diseases
• Injury to the back and pelvis
• Infection
• Tumor like conditions

Investigations and diagnosis
No test, as such, is available that is specific to ankylosing spondylitis, so the diagnosis is more or less clinical, supported by laboratory and radiological parameters. As stated earlier, 90% of patients with AS are positive for HLAB27 gene, however, HLAB27 positivity of up to 50% can be seen in the unaffected population, hence limiting its usage as a diagnostic tool. Other lab parameters that are of help are ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein), the elevation of which is suggestive of on-going chronic inflammatory process in the body. Complete blood count is often normal; however, anemia may be seen at later stage of the disease. Serologic test for rheumatoid arthritis (rheumatoid factor) is always negative; hence, it is also a part of disorders that are broadly classified as sero-negative spondyloarthropathy.
The presence of sacroilitis is one of the most important radiological parameters for diagnosis of AS. This can be seen on plain X-ray, although MRI is more sensitive in detection of disease at an early stage, and also helps to rule out other pathologies. X-rays of sacroiliac joints show signs of inflammation and erosion of bone. This feature, when the disease progresses at later stage, can be seen as sclerosis or fusion of the sacroiliac joint. X-rays of spine can demonstrate progressive straightening, squaring of vertebra, and end stage fusion of one vertebra to the next. Fusion up and down the spine leads to appearance of bamboo spine on X-ray.
When arthritis progresses to other joints like hip, knees, and shoulder, it can be seen on X-ray as loss of joint space of affected joint and osteopenia (decreased bone density on X-ray). At terminal arthritis, bony ankylosis (fusion of bones, which form a joint) is also seen on X-ray.

Treatment involves multimodal approach comprising a team of orthopedician, rheumatologist, physiotherapist, and occupational therapist.

Physical therapy: It is the most important non-pharmacological intervention in the treatment of ankylosing spondylitis. It consists of instructions and exercises to maintain proper posture and range of motion of joints. These exercises can be deep breathing exercises to maintain chest mobility and lung expansion, and stretching exercises to improve spine and joint mobility. Since patients with ankylosis of the spine tend to have forward curvature of spine (kyphosis), they are advised to maintain an upright posture as much as possible and perform spine-extension exercise. Patients are also advised to sleep on firm mattress and avoid pillow use to prevent development of deformity of spine. Physical therapists customize exercise programs of every individual, depending on the need and stage of the disease. Swimming can often be a very effective form of exercise, as it avoids jarring impact of spine. Aerobics exercise is often encouraged, as it promotes full expansion of breathing muscles and opens airways of the lungs. Cigarette smoking is strongly discouraged, as it accelerates lung scarring and rapidly worsens breathing difficulty.

Occupational therapy: People with AS may need to modify their activities of daily living and adjust features of their work place. For example, workers can modify their chairs and desks to maintain proper posture, and drivers can use wide-view rear mirrors and prism glasses to compensate limited mobility of their spine.

Rheumatologist: They are of help in use of medications to reduce inflammation and/or suppress immunity to retard the progress of the disease. Aspirin and other NSAIDs are commonly used to decrease pain and stiffness of the spine and other joints. Commonly used NSAIDs are indomethacin, naproxen, diclofenac, sulindac, etc., and their common side effects are abdominal pain, nausea, vomiting, diarrhea, and even bleeding ulcers. These medications are frequently taken after food to minimize the side effects. Those not responding to NSAIDs alone can be considered for disease modifying anti-rheumatic drugs (DMARDs), corticosteroids, or even biologic modifiers. These drugs suppress the immune system of the body and hence reduce inflammation and disease activity, thus reducing pain and improving mobility. However, these are expensive, and not free of side effects. Careful use of medications under supervision of the physician, with regular follow-up, is strongly recommended.

Orthopedic surgeon: The role of the orthopedic surgeon comes at the advanced stage of the disease, when the patient has developed ankylosis, or deformity. The aim is to improve the quality of life and prevent progressive worsening of deformity. Progressive kyphotic deformity of the spine can lead to narrowing of the spinal canal, leading to compression of the spinal cord. This needs to be corrected by surgical means. Corrective osteotomy of spine is performed at the lumbar level, because attachment of ribs to thoracic vertebra precludes corrective osteotomy at thoracic level. In this procedure, a wedge of bone from the fused vertebra is removed, and spine carefully manipulated by extension, to correct the deformity, and is fixed at this position with rods and screws at level above and below the osteotomy site. This procedure is technically demanding and carries probable risks of neurovascular injury. Other postoperative complications are paralytic ileus, acute gastric dilatation, bed sores, etc.
Patients presenting with advanced arthritis of hip and knee joint benefit from joint replacement surgery. In this procedure, the damaged part of bones forming the joint are removed and replaced with metallic implant, conferring normal articular shape and congruity with a polymeric or ceramic bearing in-between the metallic surfaces. This is also a technically challenging procedure demanding great expertise and experience. The possible complications are bleeding, infection, postoperative dislocation, stiffness, fracture, etc.

Prevention
There is no prevention, as such, for this inherited disease. The preventive measures are directed towards preventing complications of the disease with optimal treatment and monitoring side-effects of treatment. Multimodal approach to treatment and adherence to pharmacological as well as non-pharmacological modalities of treatment is the key to achieve better prognosis.

 

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