Ankylosing spondylitis (& Atlanto-axial subluxation)

• Intermittent oligoarthritis, especially in the lower extremities; hip and ankle arthritis; occasionally, inflammation of the small joints of the feet.
• night pain
• morning stiffness that is relieved by exercise
• flattening or loss of lumbar lordosis
• Localized tenderness also may be demonstrated at the insertion of the Achilles tendon or the plantar fascia.
• Although a history of low back or buttock pain should be sought, evidence of arthritis of the sacroiliac joints and spine may not be apparent for 5 to 10 years after onset.
• Extra-articular manifestations of AS are uncommon but include:
  • unilateral acute iritis
  • aortic valve insufficiency
  • atlantoaxial subluxation

Confirmation of the diagnosis of AS by laboratory studies is difficult because many results are variable and nonspecific.

• ESR may be normal or elevated.
• The platelet count also may be elevated.
• Rheumatoid factor and antinuclear antibodies are universally absent.
• Results of human leukocyte antigen (HLA) studies are probably the most diagnostic because HLA-B27 is present in up to 90% of the AS population.
• Antistreptolysin O antibody titers are not elevated in patients who have AS. This test may be useful in the diagnosis of rheumatic fever.

The primary goal is to exclude other conditions that can mimic arthritis, such as sepsis, malignancy, and trauma.

References:
Cabral DA, Malleson PN, Petty RE. Spondyloarthropathies of childhood.
Pediatr Clin North Am. 1995;42:1051-1070
Schaller JG. Juvenile rheumatoid arthritis. Pediatr Rev. 1997;18:337-349