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Chapter 355: The Spondyloarthritides

Joel D. Taurog

INTRODUCTION

The spondyloarthritides are a group of overlapping disorders that share certain clinical features, genetic associations, and pathogenic mechanisms. The classic designations include ankylosing spondylitis (AS), reactive arthritis (ReA), psoriatic arthritis (PsA) and spondylitis, enteropathic arthritis and spondylitis, juvenile-onset spondyloarthritis (JSpA), and undifferentiated SpA. More recently, these disorders have been broadly classified as predominantly axial SpA, affecting the spine, pelvis, and thoracic cage, or predominantly peripheral SpA, affecting the extremities.

ANKYLOSING SPONDYLITIS AND AXIAL SPONDYLOARTHRITIS

AS is an inflammatory disorder of unknown cause that primarily affects the axial skeleton; peripheral joints and extraarticular structures are also frequently involved. The disease usually begins in the second or third decade. The term axial spondyloarthritis (ax-SpA) is now in common use, supported by criteria formulated in 2009 (Table 355-1). This classification includes definite AS, early stages that will progress to meet classical criteria for AS, and one or more nonprogressing phenotypes. The estimated prevalence of ax-SpA in the US adult population is from 0.9 to 1.4%, similar to that of rheumatoid arthritis (RA).

TABLE 355-1ASAS Criteria for Classification of Axial Spondyloarthritis (to be applied for patients with back pain ≥3 months and age of onset <45 years)a
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TABLE 355-1 ASAS Criteria for Classification of Axial Spondyloarthritis (to be applied for patients with back pain ≥3 months and age of onset <45 years)a
Sacroiliitis on Imaging Plus ≥1 SpA Feature OR HLA-B27 Plus ≥2 Other SpA Features

Sacroiliitis on imaging

  • Active (acute) inflammation on MRI highly suggestive of SpA-associated sacroiliitisb

    and/or

  • Definite radiographic sacroiliitis according to modified New York criteriac

  

SpA features

  • Inflammatory back paind

  • Arthritise

  • Enthesitis (heel)f

  • Anterior uveitisg

  • Dactylitise

  • Psoriasise

  • Crohn’s disease or ulcerative colitise

  • Good response to NSAIDsh

  • Family history of SpAi

  • HLA-B27

  • Elevated CRPj

aSensitivity 83%, specificity 84%. The imaging arm (sacroiliitis) alone has a sensitivity of 66% and a specificity of 97%. bBone marrow edema and/or osteitis on short tau inversion recovery (STIR) or gadolinium-enhanced T1 image. cBilateral grade ≥2 or unilateral grade 3 or 4. dSee text for criteria. ePast or present, diagnosed by a physician. fPast or present pain or tenderness on examination at calcaneus insertion of Achilles tendon or plantar fascia. gPast or present, confirmed by an ophthalmologist. hSubstantial relief of back pain at 24–48 h after a full dose of NSAID. iFirst- or second-degree relatives with ankylosing spondylitis (AS), psoriasis, uveitis, reactive arthritis (ReA), or inflammatory bowel disease (IBD). jAfter exclusion of other causes of elevated CRP.

Abbreviations: ASAS, Assessment of Spondyloarthritis International Society; CRP, C-reactive protein; MRI, magnetic resonance imaging; NSAIDs, nonsteroidal anti-inflammatory drugs; SpA, spondyloarthritis.

Source: From M Rudwaleit et al: Ann Rheum Dis 68:777, 2009. Copyright 2009, with permission from BMJ Publishing Group Ltd.

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