ESSENTIALS OF DIAGNOSIS
The hallmark feature of axial spondyloarthritis (axSpA) is inflammatory back pain (IBP), especially with onset younger than 45 years of age. IBP features include worsening with rest, improvement with activity or exercise, nighttime awakening due to pain and/or stiffness (especially in the second part of the night), and response to nonsteroidal anti-inflammatory drugs (NSAIDs).
Other SpA features include enthesitis, peripheral arthritis, dactylitis, acute anterior uveitis (AAU), psoriasis, and inflammatory bowel disease (IBD).
Among Caucasian individuals with ankylosing spondylitis (AS) (radiographic axSpA), 85–95% are positive for HLA-B27. However, among those who are Black, HLA-B27 is only present in 50%.
Damage to the bilateral sacroiliac (SI) joints is seen on conventional radiographs, although this finding may only develop years after initial symptom onset. Acute inflammation (bone marrow edema) and structural lesions (erosions, ankylosis, and subchondral fat [fat metaplasia]) may be seen earlier on magnetic resonance imaging (MRI) of the SI joints.
Spondyloarthritis (SpA) encompasses a spectrum of diseases characterized by inflammation affecting the sacroiliac (SI) joints, spine, or peripheral joints (Figure 15–1). It is further subdivided into axial and peripheral predominant disease. Ankylosing spondylitis (AS) refers to axial spondyloarthritis (axSpA) with radiographic damage of the SI joints evident on conventional radiography, while nonradiographic axial spondyloarthritis (nr-axSpA) refers to disease in the absence of radiographic damage. The broader category of SpA also includes peripheral involvement, including psoriatic arthritis (PsA), reactive arthritis, and arthritis associated with inflammatory bowel disease (IBD). The terminology “seronegative spondyloarthropathy” should not be used as it refers to the absence of rheumatoid factor, which is not used in the diagnosis of SpA. Additionally, SpA is preferred over spondyloarthropathy to reflect the inflammatory process.
Spectrum of axSpA. Not all patients progression from nonradiographic axSpA to have structural damage. Per data from cohort studies, about 10% progressed at 2 years and 50% at 10 years.
The prevalence of axSpA in the United States is about 0.9–1.4% of the adult population. Inflammatory back pain (IBP), which has a prevalence of 5–6% among US adults (2009–2010 National Health and Nutrition Examination Survey [NHANES]), is the hallmark feature of axSpA. Symptom onset occurs in the third decade, and the typical male to female distribution is 1:1, though closer to 2–3:1 in the setting of radiographic axSpA (also known as AS). Hereditary factors account for most of the susceptibility of AS. In chronic low back pain, a family history of SpA adds predictive value for a diagnosis of SpA. HLA-B27 is the strongest known risk factor associated with AS, though it only accounts for 20% of the risk. The prevalence of HLA-B27 positivity among the general adult population in NHANES was 6.1%, with a prevalence of 7.5% in non-Hispanic whites and 3.5% in all other racial/ethnic backgrounds. Approximately 80–90% of individuals with AS are ...