JUVENILE ANKYLOSING SPONDYLITIS

Introduction
Childhood spondyloarthropathies generally present with involvement of large joints in the lower limbs, often with dactylitis and enthesopathy. In many cases, they are termed 'undifferentiated' without spinal involvement and many fulfil features of SEA (seronegative enthesopathy& arthropathy) syndrome. Some with undifferentiated disease develop definite sacroiliitis, leading to a diagnosis of juvenile ankylosing spondylitis. Some develop sacroiliitis much later evolving into adult AS. However, spinal involvement may develop insidiously and should be actively sought. Juvenile ankylosing spondylitis may represent up to 20 percent of cases of spondyloarthropathy.

HLA-B27 is present in 90 percent of children with JAS, but it is positive only in about 60 percent of children with undifferentiated spondyloarthropathy. HLA B-27 cannot be used to rule in or exclude the diagnosis, though its positivity in the adolescent with late onset lower limb arthritis and in anterior uveitis may alert the clinician to future spinal involvement.

Other spondyloarthropathies include the reactive arthropathies, psoriatic arthritis, and the axial arthropathy associated with inflammatory bowel disease.
Clinical features
Onset is typically in early adolescence and commonly in boys. Early symptoms may be misattributed to sporting trauma with delay in diagnosis. The typical features are lower limb asymmetric arthritis with knee effusion but ankle & hip are also commonly involved. Enthesitis (achilles tendonitis or plantar fasciitis) is a prominent feature in approximately 75 percent and dactylitis of fingers & toes may also be seen (although this is commoner in psoriatic arthritis).

Inflammatory back pain with morning stiffness must be specifically sought as children and their families often do not relate them to the presenting complaint. Swelling of small joints may also occur especially in psoriatic arthritis. Anterior uveitis, skin lesions, and gastrointestinal complaints may occur as pointers to specific diagnoses such Juvenile AS or Inflammatory Bowel Disease. However, the condition may remain undifferentiated before emergence of such specific clues
Laboratory markers
HLA-B27 has been discussed. Acute phase markers such as ESR and CRP are usually elevated with systemic or prominent peripheral joint involvement but most children have no abnormal laboratory findings. Antinuclear antibodies may be found with psoriatic arthritis and rheumatoid factor is negative.
Imaging
Radiography may show heel spurs and sacroiliitis in patients with juvenile ankylosing spondylitis but may be normal. Magnetic imaging is more sensitive and is indicated early to investigate sacroiliitis.

Associated diseases are inflammatory bowel disease, Whipple's disease, Psoriatic arthritis & Reactive arthritis. These conditions are differentiated from Juvenile AS by presence of their specific features although these manifestations may be delayed. When the hip is involved other childhood conditions such as slipped capital femoral epiphysis, Legg-Calve-Perthes disease, and osteoid osteomas need to be considered.
Children with HLA B-27, elevated ESR/CRP and systemic symptoms are more likely to have progressive disease.
Treatment
The undifferentiated spondyloarthropathies often respond well to NSAIDs. Children refractory to NSAIDs may improve with sulfasalazine. Methotrexate is sometimes indicated in systemic symptoms and severe disease.

Refractory cases despite use of sulfasalazine or methotrexate may respond to anti-tumor necrosis factor agents, etanercept or infliximab or leflunomide. Steroids are often necessary to control the extra-articular manifestations.
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