Causes of Ankylosing Spondylitis, Symptoms, Diagnosis

The information cited below is not binding. Each case should be adjudicated on the evidence provided and its own merits.

Idiopathic

• The precise etiology is unclear.

Genetic

• Although the precise cause of Ankylosing Spondylitis is unknown, there is a strong genetic component, i.e. HLA-B27.

Significant physical trauma – aggravation only

• Significant physical trauma will produce aggravation only on the site that is affected by significant physical trauma.

For significant physical trauma to produce aggravation of Ankylosing Spondylitis, the following should be evident

• Significant physical trauma must occur in an area of the body where Ankylosing Spondylitis is active;
• Increased signs/symptoms of Ankylosing Spondylitis must be present on a continuous or recurrent basis for at least 6 months.

• Significant physical trauma is a discrete injury that causes, within 24 hours of the injury being sustained, the development of acute symptoms and signs for which medical attention would normally or reasonably be sought.
• Inability to obtain appropriate clinical management

Medical conditions which are to be included in entitlement / Assessment

• Chronic mechanical lumbar/thoracic (Dorsal)/cervical Pain
• Peripheral arthritis due to ankylosing spondylitis
• Enthesitis

Common medical conditions which may result in whole or in part from ankylosing spondylitis

• Restrictive lung disease
• Cauda equina syndrome
• Post-traumatic intervertebral fractures (the C5-C6 or C6-C7 level is the most commonly involved site)
• Osteoporosis
• Uveitis
• Aortic regurgitation
• Cardiac conduction abnormalities
• Atlantoaxial subluxation
• IgA nephropathy

Diagnosis of Ankylosing Spondylitis

Early diagnosis of AS is important if fusion of the joints and permanent stiffening of the spine are to be avoided. It can be difficult to diagnose in the early stages as symptoms may be attributed to more common causes of back pain.   A doctor will evaluate the following when diagnosing the condition

• A full medical history, including any family history of AS
• Discussion of current symptoms including a history of back pain
• The age of the patient when the pain started
• Physical assessment
• Bamboo spine- Bamboo spine is a radiographic feature seen in ankylosing spondylitis that occurs as a result of vertebral body fusion. It is often accompanied by fusion of the posterior vertebral elements as well and resembles a bamboo stem…therefore the term bamboo spine.
• Schober’s test – The Schober’s test is a useful clinical measure of flexion of the lumbar spine performed during the physical examination.

A number of imaging abnormalities, especially those affecting the spine and sacroiliac joints, are characteristic of AS. In fact, according to the Assessment of Spondyloarthritis International Society (ASAS) 2009 axial SpA criteria, evidence of sacroiliitis on imaging (radiographic or MRI) is a major inclusion criteria for AS. A standardized plain radiographic grading scale exists for sacroiliitis, which ranges from normal (0) to most severe (IV), as detailed below.

• 0: Normal SI joint width, sharp joint margins
• I: Suspicious
• II: Sclerosis, some erosions
• III: Severe erosions, pseudo dilation of the joint space, partial ankylosis
• IV: Complete ankylosis

In the first few years of AS, plain radiographic changes in the SI joints can be very subtle, but within the first decade will usually become more obvious. Subchondral erosions, sclerosis, and joint fusion are the most obvious abnormalities, and these radiographic changes are typically symmetric.

These diagnostic criteria include

Inflammatory Back Pain

Chronic, inflammatory back pain is defined when at least four out of five of the following parameters are present-

• Age of onset below 40 years old,
• Insidious onset,
• Improvement with exercise, or not?
• no improvement with rest
• pain at night (with improvement upon getting up)

• Past history of inflammation in the joints, heels, or tendon-bone attachments
• Family history for axial spondyloarthritis
• Positive for the biomarker HLA-B27
• Good response to treatment with nonsteroidal anti-inflammatory drugs (NSAIDs)
• Signs of elevated inflammation (C-reactive protein and erythrocyte sedimentation rate)
• The manifestation of psoriasis, inflammatory bowel disease, or inflammation of the eye (uveitis)
• X-rays
• MRI (magnetic resonance imaging)
• Blood tests – which may show the presence of the HLA-B27gene, a raised ESR (erythrocyte sedimentation rate) and a reactive protein which indicates inflammation
• A drawback of X-ray – diagnosis is the signs and symptoms of AS have usually been established as long as 8–10 years prior to X-ray-evident changes occurring on a plain film X-ray, which means a delay of as long as 10 years before adequate therapies can be introduced. Options for earlier diagnosis are tomography and MRI of the sacroiliac joints, but the reliability of these tests is still unclear.
• Genetic testing – Variations of the HLA-B gene increase the risk of developing ankylosing spondylitis, although it is not a diagnostic test. Those with the HLA-B27 variant are at a higher risk than the general population of developing the disorder. HLA-B27, demonstrated in a blood test, can occasionally help with diagnosis, but in itself is not diagnostic of AS in a person with back pain. Over 90% of people that have been diagnosed with AS are HLA-B27 positive, although this ratio varies from population to population (about 50% of African Americans with AS possess HLA-B27 in contrast to the figure of 80% among those with AS who are of Mediterranean descent

In order for a diagnosis of AS to be made, a referral to a rheumatologist – who specializes in treating arthritis – may be recommended.

References

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