Spondyloarthritis (SpA), also known as spondyloarthropathy, is a collection of inflammatory rheumatic syndromes connected by genetic predisposition and clinical symptoms. The best-known subtypes are enteropathic arthritis (EA), psoriatic arthritis (PsA), ankylosing spondylitis (AS), and reactive arthritis (ReA). Symptoms of spondyloarthritis include back pain, arthritis, and enthesitis, inflammation at bone-adhering ligaments, tendons, or joint capsules. Spondyloarthritis is caused by a combination of genetic and environmental factors. It is associated with intestinal inflammation, with a connection between Crohn's disease and ankylosing spondylitis. Reactive arthritis is primarily caused by gastrointestinal, genitourinary, respiratory infections, and genetic factors. Spondyloarthritis is diagnosed based on symptoms and imaging. Early diagnosis criteria use genetic testing and more advanced forms of medical imaging. Spondyloarthritis is categorized into two groups based on the Assessment of SpondyloArthritis International Society (ASAS) criteria: primarily axial involvement and predominantly peripheral manifestations. Non-steroidal anti-inflammatory drugs (NSAIDs) are administered first for active axial signs of spondyloarthritis. If NSAIDs are contraindicated or cause side effects, TNF blockers are used. Traditional disease-modifying antirheumatic drugs (DMARDs) are not used for people without peripheral disease signs.
Signs and symptoms In all subtypes of spondyloarthritis, inflammatory back pain and/or asymmetrical arthritis, mainly affecting the lower limbs, are the most common symptoms. Another characteristic is enthesitis, which is inflammation at the locations where ligaments, tendons, or joint capsules adhere to bone.
Inflammatory back pain associated with ankylosing spondylitis usually starts slowly, has a dull feel to it, and spreads into the gluteal areas. Back pain has a nocturnal component, gets better with movement, and is worse in the morning. Axial arthritis may begin in the sacroiliac joints and work its way up to the cervical spine over time. Spinal abnormalities such as flattening of the lumbar lordosis, exaggeration of the thoracic kyphosis, and hyperextension of the cervical spine lead to limited spinal motion. Hip and shoulder arthritis can occur in some people with ankylosing spondylitis, usually early in the course of the illness. Usually, the other peripheral joints start to be affected later. Most frequently, there is an asymmetrical involvement of the lower extremities. Reactive arthritis is an aseptic arthritis caused by an infectious pathogen found outside the joint. Particularly affecting the joints in the lower limbs, the arthritis is usually oligoarticular. In most cases, the condition develops quickly; two to four joints may swell and hurt in an uneven manner within a few days. Inflammatory back pain and dactylitis are also prevalent. Psoriatic arthritis is known to present in five distinct patterns: oligoarticular (affecting four or fewer joints); polyarticular (affecting five or more joints); prominent distal interphalangeal (DIP) joint involvement; arthritis mutilans; and psoriatic spondylitis. More than 70% of cases follow the oligoarticular pattern. Distal joints are frequently impacted by psoriatic arthritis, which is typically asymmetrical. Up to 20% of people with inflammatory bowel disease (IBD) develop spondyloarthropathy. Those with Crohn's disease are more likely to have this association than those with ulcerative colitis. Arthritis may appear before bowel disease. Usually, the lower extremities are asymmetrically affected by arthritis. The arthritis typically manifests abruptly and follows a migratory pattern. In those who do not fit the criteria for any of the well-established spondyloarthropathies, the term "undifferentiated spondyloarthropathy" is used to characterize the signs of spondyloarthritis. A tiny percentage of these eventually experience a characterized spondyloarthritis, but most experience more general symptoms such as dactylitis, enthesitis, unilateral or alternating buttock pain, inflammatory back pain, and occasionally extra-articular symptoms.
Causes Spondyloarthritis is caused by a complicated combination of genetic polymorphisms and environment. The relative contributions of genes and environment may differ across different types of spondyloarthritis.
Risk factors Microscopically visible ileal inflammation is seen in about 50% of people with spondyloarthritis and ankylosing spondylitis during ileocolonoscopy. There seems to be an immunological connection between the gut inflammation observed in Crohn's disease and ankylosing spondylitis. It is known that, in comparison to healthy controls, people with ankylosing spondylitis and those related to them have higher intestinal permeability.
Triggers The majority of organisms responsible for reactive arthritis are gastrointestinal pathogens, such as Shigella flexneri, Clostridioides difficile, Yersinia enterocolitica and Yersinia pseudotuberculosis, Campylobacter jejuni and Campylobacter coli, and Salmonella spp. Genitourinary and respiratory infections, such as Chlamydia trachomatis and Chlamydia pneumoniae, have also been linked to reactive arthritis.
Genetics Given the well-established familial aggregation and the concordance rate of up to 63% in identical twins (vs 23% in nonidentical twins), it is evident that genetic variables play a role in the susceptibility to ankylosing spondylitis. There is limited research on familial aggregation in other forms of spondyloarthritis. HLA-B27 is a polymorphic form of the HLA-B molecule found in up to 95% of people with ankylosing spondylitis of European ancestry, 70% with reactive arthritis, 60% with psoriatic spondylitis, 25% with peripheral psoriatic arthritis, and 70% with spondylitis associated with inflammatory bowel disease.
Mechanism
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