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Chapter 60: Pediatric Musculoskeletal Medicine

Heakyung Kim; Hannah A. Shoval

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JUVENILE IDIOPATHIC ARTHRITIS

Introduction

Juvenile idiopathic arthritis (jia) is a chronic inflammatory condition defined by the International League of Associations for Rheumatology (ILAR) as arthritis that begins before the age of 16 years and persists for at least 6 weeks with exclusion of other known conditions.1 JIA is divided into systemic arthritis, oligoarthritis, polyarthritis, psoriatic arthritis, enthesitis-related arthritis, and undifferentiated arthritis (Table 60–1).2

Table 60–1Classification on Juvenile Idiopathic Arthritis
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Table 60–1 Classification on Juvenile Idiopathic Arthritis
Type of JIA Definition
Systemic arthritis:

Arthritis and fever for 2 or more weeks and either

  1. Evanescent erythematous rash

  2. Generalized lymph node enlargement

  3. Hepatomegaly and/or splenomegaly

  4. Serositis
Oligoarthritis Arthritis in one to four joints during first 6 months
Polyarthritis (RF negative or positive) Arthritis in five or more joints in first 6 months
Psoriatic arthritis

Arthritis and

  • Psoriasis

or

  • Two or more of the following: dactylitis, nail pitting, or onycholysis or psoriasis in a first-degree relative
Enthesitis-related arthritis

Arthritis and enthesitis or arthritis or enthesitis with two or more of the following:

  • SI joint tenderness/inflammatory lumbosacral pain

  • HLA-B27

  • Onset of arthritis in males ≥6 years of age

  • Acute anterior uveitis

  • History of ankylosing spondylitis, enthesitis-related arthritis, sacroiliitis with inflammatory bowel disease, Reiter's syndrome, or acute anterior uveitis in a first-degree relative
Undifferentiated arthritis Fulfills criteria for no category or two or more categories

Source: Harris JG, Kessler EA, Verbsky JW. Update on the treatment of juvenile idiopathic arthritis. Curr Allergy Asthma Rep. 2013;13(4):337–346. doi:10.1007/s11882-013-0351-2.

Epidemiology

In a systematic review, incidence rates varied from 1.6 to 23 per 100,000 persons and prevalence from 3.8 to 400 per 100,000 persons.3 Pooled incidence and prevalence were about doubled for girls.

Pathophysiology

Inflammation of the joints is thought to be related to polymorphisms in human leukocyte antigens that lead to antigen-activated T cells that release cytokines.4 This stimulates chondrocytes, osteoclasts, and fibroblasts to release metalloproteinases, leading to the erosion of bone and cartilage, synovial joint inflammation, and pannus formation.4

History and Physical Examination

In addition to a detailed history of joint pain, systemic features such as duration of fever, serositis, acute anterior uveitis, and lymphadenopathy are also important to ask about.4 A family medical history of psoriasis or rheumatologist conditions, especially ankylosing spondylitis, enthesitis-related arthritis, sacroiliitis with inflammatory bowel disease, Reiter's syndrome, and acute anterior uveitis, is particularly helpful.4,11

Objective: Laboratory Tests/Radiology

Laboratory Tests

Leukocytosis, thrombocytosis, and anemia are common in the condition.5 Inflammatory markers may be elevated, including the erythrocyte sedimentation rate (ESR), C-reactive protein, or ferritin. Rheumatoid factor (rarely seen in children younger than age 10),6 anti-cyclic citrullinated peptide antibodies, ...

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