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Ankylosing Spondylitis and Other Spondyloarthritides


The diseases collectively referred to as spondyloarthritides include ankylosing spondylitis (AS) , arthritis associated with inflammatory bowel disease (IBD) or psoriasis, and reactive arthritis following gastrointestinal (GI) or genitourinary (GU) infections ( Table 181.1 and Table 181.2 ). Spondyloarthritis is more common in adults, but all forms can present during childhood with varying symptoms and signs. Many children with spondyloarthritis are classified in the juvenile idiopathic arthritis (JIA) categories of enthesitis-related arthritis (ERA) or psoriatic arthritis. Children and adolescents with spondyloarthritis who may not meet JIA criteria include arthritis associated with IBD, juvenile ankylosing spondylitis (JAS), and reactive arthritis.

Table 181.1
Overlapping Characteristics of the Spondyloarthritides *
From Cassidy JT, Petty RE: Textbook of pediatric rheumatology, ed 6, Philadelphia, 2011, Elsevier/Saunders.
CHARACTERISTIC JUVENILE ANKYLOSING SPONDYLITIS JUVENILE PSORIATIC ARTHRITIS INFLAMMATORY BOWEL DISEASE REACTIVE ARTHRITIS
Enthesitis +++ + + ++
Axial arthritis +++ ++ ++ +
Peripheral arthritis +++ +++ +++ +++
HLA-B27 positive +++ + ++ +++
Antinuclear antibody positive − ++ − −
Rheumatoid factor positive − − − −
SYSTEMIC DISEASE:
Eyes + + + +
Skin − +++ + +
Mucous membranes − − + +
Gastrointestinal tract − − ++++ +++

* Frequency of characteristics: −, absent; +, <25%; ++, 25–50%; +++, 50–75%; ++++, ≥75%.

Table 181.2
From Kim PS, Klausmeier TL, Orr DP: Reactive arthritis: a review, J Adolesc Health 44:309–315, 2009 (Table 2, p 311).
Etiologic Microorganisms of Reactive Arthritis

Probable

  • Chlamydia trachomatis

  • Shigella species

  • Salmonella enteritidis

  • Salmonella typhimurium

  • Yersinia enterocolitica

  • Yersinia pseudotuberculosis

  • Campylobacter jejuni and coli

Possible

  • Neisseria gonorrhoeae

  • Mycoplasma fermentans

  • Mycoplasma genitalium

  • Ureaplasma urealyticum

  • Escherichia coli

  • Cryptosporidium

  • Entamoeba histolytica

  • Giardia lamblia

  • Brucella abortus

  • Clostridium difficile

  • Streptococcus pyogenes

  • Chlamydia pneumoniae

  • Chlamydia psittaci

Epidemiology

JIA is diagnosed in 90 per 100,000 U.S. children every year (see Chapter 180 ). ERA accounts for 10–20% of JIA, and has a mean age at onset of 12 yr. In India, ERA is the most common category of JIA, accounting for 35% of cases. Unlike other JIA categories, males are affected more often than females, accounting for 60% of ERA cases. AS occurs in 0.2–0.5% of adults, with approximately 15% of cases beginning in childhood. These disorders can be familial, largely as a result of the influence of human leukocyte antigen ( HLA ) -B27 , which is found in 90% of JAS and 50% of ERA patients compared to 7% of healthy individuals. Approximately 20% of children with ERA have a family history of HLA-B27–associated disease, such as reactive arthritis, AS, or IBD with sacroiliitis.

Etiology and Pathogenesis

Spondyloarthritides are complex diseases in which susceptibility is largely genetically determined. Only 30% of heritability has been defined, with HLA-B27 responsible for two thirds of the total, and >100 additional genetic loci accounting for only one third. Genes that influence interleukin (IL)-23 responses (e.g., CARD9 , IL23R, JAK2, TYK2 , STAT3 ) and the function of HLA-B27 (ERAP1) are particularly important. Unusual properties of HLA-B27, such as its tendency to misfold and form abnormal cell surface structures, may have a role. Infection with certain GI or GU pathogens can trigger reactive arthritis (see Table 181.2 and Chapter 182 ). Altered gut microbiota and an abnormal immune response to normal microbiota may also play a role in pathogenesis. Inflamed joints and entheses in spondyloarthritis contain T and B cells, macrophages, osteoclasts, proliferating fibroblasts, and osteoblasts, with activation of the IL-23/IL-17 pathway. Bone loss and osteoproliferation in and around vertebral bodies and facet joints in long-standing AS contribute to significant morbidity.

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