ABSTRACT: Spondyloarthritis (SpA) disorders have shared clinical features and are related clinically and genetically but are distinct entities. The Assessment of SpondyloArthritis international Society (ASAS) has developed new classification criteria for axial SpA and peripheral SpA; the older criteria did not specifically differentiate between them. The New York criteria were developed before the routine use of MRI in clinical medicine, making sacroiliitis on plain radiographs an essential element and leading to poor sensitivity and a delay in diagnosis. The new ASAS criteria for axial SpA are designed to help clinicians make an earlier diagnosis and facilitate clinical trials. Classification criteria are meant to be applied in clinical trials but also are helpful in establishing a diagnosis in patients who are referred to a rheumatology practice. (J Musculoskel Med. 2011;28:454-457)
The spectrum of spondyloarthritis (SpA) disorders—typically including ankylosing spondylitis (AS), arthritis associated with inflammatory bowel disease (IBD), reactive arthritis, psoriatic arthritis, and undifferentiated SpA—are related clinically and genetically but are distinct entities. Shared clinical features include inflammatory back pain (IBP); oligoarticular and asymmetrical peripheral arthritis, with a lower limb predilection; enthesitis; dactylitis; and uveitis. To varying degrees, SpA disorders are associated with the HLA-B27 gene, supporting a genetic basis.1,2 They also may be categorized according to their predominant clinical manifestations as involving primarily axial symptoms (IBP in the sacroiliac joints or spine or both) or peripheral symptoms (peripheral arthritis, enthesitis, and dactylitis), with possible overlap.
Recently, the Assessment of SpondyloArthritis international Society (ASAS) developed new classification criteria for both axial SpA and peripheral SpA. Although SpA conditions have the many similarities described above, they also have several genetic, prognostic, and therapeutic differences. Therefore, grouping together all “peripheral SpA” under 1 umbrella is open for criticism from specialists, who tend to be “splitters” rather than “lumpers.”
This is the second in a series of articles that describe new or modified classification and diagnostic criteria for various rheumatologic conditions. The first article (“New classification criteria for RA,” The Journal of Musculoskeletal Medicine, November 2011) discussed recent revisions in rheumatoid arthritis classification criteria. In this article, we review the new classification criteria for SpA.
The need for new criteria
Two of the older sets of criteria frequently used to make a diagnosis of SpA—the Amor criteria3 and the European Spondyloarthropathy Study Group (ESSG) criteria4—did not specifically differentiate between peripheral SpA and axial SpA. However, the modified New York criteria were developed specifically to classify patients with AS, but not other SpA subtypes.
The New York criteria were developed in 1984, before the routine use of MRI in clinical medicine; therefore, sacroiliitis on plain radiographs is an essential element.2 However, this requirement inherently leads to poor sensitivity for classifying early disease and results in a delay in diagnosis—it may take up to 6 to 8 years for sacroiliitis to become apparent on plain radiographs after the onset of IBP. Also, by the time sacroiliitis is apparent on plain radiographs, it reflects “joint damage” rather than “active inflammation.”1,5
More recently, MRI has dramatically improved the imaging of sacroiliitis with or without structural damage. The new ASAS criteria for axial SpA are designed to help clinicians make an earlier diagnosis in patients with or without radiographic sacroiliitis and facilitate clinical trials with such patients.6 In addition, the new ASAS criteria for peripheral SpA meet a need for specific criteria for this subgroup, which had been lacking.7
The process of developing new criteria
For the development of axial SpA classification criteria, 20 internationally recognized experts in the field of SpA (all ASAS members) reviewed 71 “paper patients”—including those without radiographic sacroiliitis—to draft candidate criteria based on clinical reasoning. The criteria were tested, refined, and validated in a large prospective study cohort of 649 patients worldwide. For eligibility, patients were required to have had at least 3 months of chronic back pain that started before age 45 years, with or without peripheral symptoms. To avoid selection bias, the investigators enrolled patients in a consecutive manner and provided them with a diagnostic workup that included a history, examination, laboratory testing (including the HLA-B27 gene), and imaging (radiography and MRI).