Overview of Spondyloarthropathies
Spondyloarthropathy (or spondyloarthritis) is an umbrella term for a group of inflammatory rheumatic diseases. Spondyloarthropathies are progressive and painful. They often involve the axial skeleton (i.e. the spine and the sacroiliac joints), but they can also affect the peripheral skeleton. They are associated with enthesitis (inflammation of the site where tendons / ligaments insert into bone) and dactylitis (i.e. diffuse swelling of the digits). Other areas affected include the heart, eyes, lungs, skin, gut and genitourinary tract.
There are five types of spondyloarthritis:
- Axial spondyloarthritis (also known as ankylosing spondylitis)
- Psoriatic arthritis (also known as peripheral spondyloarthritis)
- Reactive arthritis (formerly called Reiter's syndrome)
- Enteropathic arthritis
- Undifferentiated spondyloarthritis
Epidemiology / Aetiology
Symptoms associated with spondyloarthropathy typically start before the age of 45. They affect men and women almost equally, with a 1.1:1 (male:female) ratio although men tend to be younger at diagnosis than women. With a prevalence rate of 0.5-1.9 percent, they are one of the most common rheumatic diseases - as common as rheumatoid arthritis. However, unlike other rheumatic diseases, spondyloarthropathies are seronegative for rheumatoid factor.
The aetiology and pathogenesis of spondyloarthropathies is complex and not fully understood. There is an initial systemic inflammatory response to a known or unknown source, which causes local tissue changes. These changes can be long-lasting in the local joint environment and the persistent inflammation causes a cycle of unbalanced bone remodelling and axial bone loss.
While the cause of spondyloarthropathy is not known, research suggests that there are environmental and genetic triggers. In particular, spondyloarthropathies have been found to share genetic links with the HLA-B27 gene. 90 percent of patients presenting with axial spondyloarthritis have this gene. However, having this gene is not, in itself, diagnostic of spondyloarthropathy as five to ten percent of patients who carry the HLA-B27 gene do not go on to develop these conditions.
Characteristics / Clinical Presentation
Back pain is extremely prevalent, so it is important to be able to differentiate between different types of back pain (i.e. mechanical or inflammatory). as well as the different types of spondyloarthropathy. The specific features of each type of spondyloarthropathy are discussed below.
Axial spondyloarthritis refers to patients who have both non-radiographic and radiographic axial spondyloarthritis. Radiographic axial spondyloarthritis is also called ankylosing spondylitis. While non-radiographic axial spondyloarthritis does not show on x-ray, there are changes on MRI.
Axial spondyloarthritis tends to start when patients are aged in their 20s. There is a male to female ratio of 2:1 for radiographic axial spondyloarthritis and of 1:1 for non-radiographic axial spondyloarthritis.
Axial spondyloarthritis predominantly affects the spine, with inflammatory changes causing pain, stiffness and a loss of motion in the back. Patients will often present with impaired spinal movement, abnormal posture, buttock and hip pain, peripheral arthritis, enthesitis and dactylitis.
It has been estimated that axial spondyloarthritis has 90 percent heritabilty, with the HLA-B27 gene being the most significant genetic factor. The actual role of HLA-B27 in the pathogenesis of axial spondyloarthritis remains unclear, but evidence suggest that the cytokines tumour necrosis factor (TNF)-α and interleukin-17 are involved.
Radiographic axial spondyloarthritis has also been linked to an increased risk of cardiovascular disease, potentially due to the systemic inflammation associated with this condition. Because it results in diminished chest wall expansion and decreased spinal mobility, it can lead to a restrictive pulmonary pattern in individuals with this condition. These individuals are also more prone to vertebral fragility fractures, atlantoaxial subluxation, spinal cord injury and, occasionally, cauda equina syndrome.
For more information on axial spondyloarthritis, please click here.
Psoriatic Arthritis (PsA) is a chronic, immune-mediated inflammatory joint disease that is associated with psoriasis. Individuals present with joint and entheses inflammation in both the axial skeleton and peripheral joints. It affects multiple organs, including the skin and is associated with increased risk of mortality from cardiovascular disease.
There is a wide variation in annual incidence of PsA, ranging from 0.1 to 23.1 cases per 100,000. Prevalence rates also vary between countries, as does the mean age at diagnosis (40.7 to 52.0 years).
Hallmark features of PsA are:
- The presence of psoriasis
- Inflammatory arthritis
- Absence of serological tests for rheumatoid arthritis
Between 60 and 70 percent of patients will develop psoriasis prior to PsA. However, in 15 to 20 percent of patients, symptoms of arthritis develop first. For 15 to 20 percent of individuals, psoriasis and arthritis will begin within a year of each other.
For more information on PsA, please click here.
Enteropathic Arthritis (EnA) is a spondyloarthropathy that occurs in patients who also have inflammatory bowel disease (IBD) and / or other gastrointestinal disease, such as ulcerative colitis and Crohn’s disease.
There is no gold standard test for EnA, so diagnosis generally relies on medical history and physical examination. Typically, patients who have IBD and then go on to develop inflammatory back pain and / or synovitis (predominantly in the lower limbs) are diagnosed as having spondyloarthropathy. Women are more likely to have peripheral joint involvement, whereas men are more likely to experience axial skeleton symptoms.
Between 17 and 39 percent of patients with IBD develop rheumatic manifestations. Between two and 16 percent of IBD patients develop EnA in the axial skeleton. The prevalence of sacroiliitis in this population is between 12 and 20 percent of patients.
Like other spondyloarthropathies, there is an association with the HLA-B27 gene, ranging from 3.9 to 18.9 percent, but the pathogenesis is not fully understood. However, it has been observed that joint inflammation occurs in patients who are genetically predisposed and who have bacterial gut infections. This, therefore, suggests that there is some relationship between inflammation of the gut mucosa and arthritis.
For more information on EnA, please click here.
Reactive arthritis (ReA) is a seronegative spondyloarthropathy, which occurs after an extra-articular infection (usually of the gastrointestinal or genitourinary tract). It is associated with inflammatory back pain, oligoarthritis, and extra-articular symptoms. It tends to develop between one and six weeks after a urogenital or gastrointestinal infection.
A classic triad of symptoms have been identified, which are:
Dermatological manifestations (such as keratoderma blennorrhagicum, circinate balanitis, ulcerative vulvitis, changes in nails, and oral lesions) can occur. It can also affect the heart and eyes although symptom severity is varied.
ReA is more common in men and typically affects young adults. Its exact pathophysiology is not yet understood, but it appears likely that infectious and immune factors are involved. Again, those affected are more likely to carry the HLA-B27 gene.
- Systemic signs of infection
For more information on ReA, please click here.
The diagnosis of undifferentiated spondyloarthropathy is used in cases where individuals exhibit features of spondyloarthropathy, but they do not fit into any of the conditions discussed above. It usually occurs in less than five joints, but generally will include the knee joint.
Spondyloarthropathy is an umbrella term that encompasses five inflammatory rheumatic diseases. These conditions can impact multiple areas of the body, including joints and entheses, as well as other organs.
While the specific aetiology remains unknown, current research suggests a strong genetic component, as well as specific environmental triggers.
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