Juvenile Idiopathic Arthritis

CHAPTER 74

Juvenile Idiopathic Arthritis

Introduction/Etiology/Epidemiology

• The term juvenile idiopathic arthritis (JIA) replaced the older term, juvenile rheumatoid arthritis, to reflect the unknown (idiopathic) cause of this disease.

• JIA is characterized by the presence of arthritis in a child younger than 16 years of age and that lasts at least 6 weeks and has no other identifiable cause.

• Annual incidence is approximately 10 per 100,000 children. Conservative estimates suggest that 300,000 children in the United States have JIA.

• JIA is an autoimmune disease. Complex interactions between the immune system and numerous environmental factors in a genetically susceptible individual result in immune-mediated inflammation of the synovial lining of joints and tendons.

• There are 7 different subtypes of JIA: oligoarticular JIA, polyarticular JIA (rheumatoid factor [RF] negative), polyarticular JIA (RF positive), enthesitis-related arthritis (ERA), psoriatic JIA, systemic JIA, and undifferentiated JIA.

• The subtypes are defined based on the number and type of joints involved, extra-articular features, family history, and laboratory profile.

• Anterior chamber uveitis is the most common extra-articular manifestation of JIA.

Signs and Symptoms

• Signs and symptoms are specific to the JIA subtype (Table 74-1).

• In young children, pain is often not a prominent feature of the disease. Morning stiffness and gait abnormalities are more common presenting features in this population.

Differential Diagnosis

• Table 74-2 lists non-JIA diagnoses associated with joint pain and/or swelling.

Diagnostic Considerations

• Arthritis is a clinical diagnosis and is characterized by the following features:

— Joint swelling

— Warmth of the skin overlying the joint

— Limitation in range of motion of the joint

— Pain on movement of the joint

• Muscle atrophy and joint contractures may also be present in cases of long-standing, undertreated disease.

Table 74-1. Signs and Symptoms of Juvenile Idiopathic Arthritis Subtypes

Abbreviations: ANA, antinuclear antibody; ERA, enthesitis-related arthritis; ESR, erythrocyte sedimentation rate; F, female; HLA, human leukocyte antigen; IBD, inflammatory bowel disease; IL, interleukin; JIA, juvenile idiopathic arthritis; M, male; MAS, macrophage activation syndrome; RF−, rheumatoid-factor negative; RF+, rheumatoid-factor positive; SI,

Table 74-2. Other Diagnoses Associated With Joint Pain and/or Swelling

Abbreviations: ASO, antistreptolysin O titer; CBC, complete blood cell count; CRP, C-reactive protein; DNase, deoxyribonuclease; ESR, erythrocyte sedimentation rate; F, female; IBD, inflammatory bowel disease; M, male; NSAIDs, nonsteroidal anti-inflammatory drugs; SI, sacroiliac; TNF, tumor necrosis factor; WBC, white blood cell.

• Enthesitis

— Inflammation at the site of attachment of a ligament, tendon, or joint capsule to bone.

— Commonly affected sites in children include the heel and foot, at the sites of insertion of both the Achilles tendon (Figure 74-1) and plantar fascia, and the knee, at the sites of attachment of the quadriceps and patellar tendons.

— Can sometimes be mistaken for noninflammatory apophysitis

— Seen in both ERA and psoriatic JIA

• Tenosynovitis

— Inflammation of the tendon sheath

— The extensor tendons of the wrist, the flexor tendons of the fingers and toes, and the flexor and extensor tendons of the ankle are typical sites of tenosynovitis in JIA.

— Can occur in all types of JIA. Tenosynovitis of the ankle tendons is common in children with oligoarticular JIA. Up to one-third of patients with ankle swelling will have tenosynovitis but not JIA (Figures 74-2 and 74-3).

• The diagnosis of JIA is unlikely if a child has normal physical examination findings.

• Temporomandibular joint (TMJ) arthritis

— Up to 78% of patients with JIA have TMJ involvement.

— Those with oligoarticular JIA and RF-negative polyarticular JIA are at highest risk.

— TMJ arthritis is often asymptomatic.

Figure 74-1. A, Ultrasonographic image shows normal Achilles enthesis (yellow line shows length of enthesis). B, Achilles enthesitis (color Doppler signal within tendon close to its insertion), with erosive changes to the calcaneus (yellow arrow) and thickening of the Achilles tendon (orange arrow).

Figure 74-2. Ankle swelling in a 5-year-old girl with oligoarticular juvenile idiopathic arthritis. Note the fullness around the anterior ankle, suggestive of a tibiotalar effusion, as well as around the lateral malleolus, suggestive of tenosynovitis of the lateral ankle tendons.

Figure 74-3. Tenosynovitis of the flexor tendons. A, Medial transverse view at the level of the medial malleolus shows an anechoic rim around the posterior tibial tendon and the flexor digitorum (yellow arrows) with positive color or power Doppler ultrasonography. B, Longitudinal ultrasonographic image of the same tendons. Note the wavy anechoic material above the posterior tibial tendon (yellow arrow).

— Physical examination findings can be very subtle and include

■Mild mandibular asymmetry with oral excursion (Figure 74-4)

■Slight micrognathia

— Magnetic resonance imaging (MRI) with and without contrast is the reference standard for evaluating TMJ synovitis (Figure 74-5).

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