Last updated: October 31, 2014
Synonyms: SpA; seronegative SpA; spondyloarthropathy, HLA-B27-related SpA. NB. The preferred terminology has
ICD-9 Codes: Spondyloarthropathy/Spondylitis, 720.9; Codes for individual disorders: AS, 720.0; reactive arthritis / Reiter ’s syndrome, 099.3; psoriatic arthritis, 696.0.
ICD-10 codes: Spondyloarthopathy/spondyloarthritis M45-M49; Ankylosing spondylitis M45; reactive arthritis/Reiter’s syndrome M02.3; juvenile ankylosing spondylitis M08.1
Definition: SpA is a generic term applied to a group of disorders characterized be a constellation of shared clinical, radiographic, and immunogenetic features. These disorders include ankylosing spondylitis (AS), reactive arthritis (formerly known as Reiter’s syndrome), psoriatic arthritis, and arthritis associated with inflammatory bowel disease (Crohn’s disease, ulcerative colitis; also known as enteropathic arthritis). Some patients manifest complete or classic findings of one of these individual disorders, while others demonstrate incomplete or overlapping features. In past years, patients with SpA features who did not fit a specific condition were sometimes designated as having ‘incomplete’ or ‘undifferentitated’ SpA. Various criteria for the diagnosis and/or classification of SpA have been developed over the years (e.g., Table 44). More recently, it has been suggested that the terms “axial spondyloarthritis” and “peripheral spondyloarthritis” be used to encompass this group of disorders.
Etiology: Because of a common association with HLA-B27, immunopathophysiologic similarities, and overlapping clinical and radiographic features, the disorders are presumed to share a similar etiopathogenesis. Proposed theories include infectious inciting events occurring in a genetically susceptible host, leading to either molecular mimicry or a chronic, antigen-driven reactive condition.
Demographics: Overall, SpA may have a prevalence of 0.5 – 2% of the population. SpAs are more likely to be seen in men. Most patients present between the ages of 20 and 50 years.
Pathology: These disorders share a common pathologic profile, which includes a propensity for axial and peripheral inflammatory arthritis and inflammation involving the eye (conjunctivitis, uveitis), skin (psoriasis, nail changes), mucosal surfaces (oral and genital), and tendinous attachments to bone (enthesitis). Synovial membranes show histologic inflammation similar in some ways but with clear differences from that seen in RA. Different than RA, in SpA there is a greater propensity for fibrous ankylosis, osseous resorption, and heterotopic bone formation.
Cardinal Findings: The SpA share a constellation of characteristic clinical, radiographic, and immunogenetic manifestations that suggest a common or related etiopathogenesis (Table 44). Distinctive features include a propensity for axial arthritis (sacroiliitis and spondylitis); peripheral arthritis (often asymmetric and oligoarticular); inflammation at tendinous, ligamentous, or fascial insertions (enthesitis); and a familial pattern of inheritance based on the presence of the class I major histocompatibility complex antigen HLA-B27. These disorders can manifest extraarticular features that suggest a particular SpA. Extraarticular manifestations may involve periarticular structures (enthesitis), eyes (uveitis), GI tract (oral ulcerations, asymptomatic gut inflammation), genitourinary tract (urethritis), cardiac involvement (aortitis, heart block), dermatologic involvement (psoriasis, keratoderma blennorrhagica).
Diagnostic Criteria: Criteria for the diagnosis of an SpA were developed by the European Spondyloarthropathy Study Group (Table 44). The criteria of Amor et al. perform equally well in population studies. These were devised because other disease-specific criteria (e.g., Rome criteria for AS) exclude many patients with SpA. Diagnostic criteria for “axial spondyloarthritis” and “peripheral spondyloarthritis” have been developed by the ASAS group (www.asas-group.org/). Broader definitions used in criteria allow for earlier diagnosis, greater inclusion in clinical trials, and earlier therapy.
Imaging: Radiographic abnormalities are similar to those seen in AS and reactive arthritis. There is a propensity for sacroiliitis, spondylitis, peripheral arthritis with soft tissue swelling, juxtaarticular osteopenia, joint space narrowing, or ill-defined erosions. Areas of periostitis, reactive new bone formation, or osteitis are not uncommon.
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