Stat Consult: Polyarticular Juvenile Idiopathic Arthritis – Clinical Advisor

Description

• Polyarticular JIA is defined as chronic (>6 weeks) inflammatory arthritis in children <16 years old involving ≥5 joints during the first 6 months of illness
• 2 subtypes:
  • Rheumatoid factor (RF)-positive subtype
    • Resembles adult rheumatoid arthritis
    • Symmetrically affecting small joints
    • Higher risk of rheumatoid nodules
    • Overall poor functional outcome
  • RF-negative subtype
    • Typically asymmetric
    • Higher risk of uveitis
    • Fewer rheumatoid nodules

Epidemiology

• JIA is one of the most common chronic diseases in children
  • Reported prevalence of 3.8 to 400 cases per 100,000 children
  • Reported incidence of 1.6 to 23 new cases per 100,000 children per year
• Approximate prevalence of International League of Associations for Rheumatology (ILAR) subtypes among children with JIA
  • Oligoarticular 50%-60%
  • Polyarticular 30%-35%
  • Systemic-onset 10%-20%
  • Psoriatic 2%-15%
  • Enthesitis-related 1%-7%
• Reported frequency of polyarticular subtypes among all JIA
  • 2%-7% for rheumatoid factor (RF)-positive polyarthritis
  • 11%-28% for RF-negative polyarthritis
• Possible risk factors include
  • Human leukocyte antigen (HLA) associations; increased likelihood for
    • RF-positive polyarthritis with DRB1*04, DQA1*03, DQB1*03
    • RF-negative polyarthritis with A2, DRB1*08, DQA1*04, DPB1*03
  • Increased antibiotic exposure in infancy

Etiology and Pathogenesis

• Complex disease with multiple environmental and genetic risk factors 
• Cause of JIA appears to be breakdown in immunologic self-tolerance
• Increasing evidence for role of the microbiome (involved in immune system development/function)
  • Changes in microbiome composition similar to those seen in other autoimmune diseases (type I diabetes, inflammatory bowel disease)
  • Early exposure to antibiotics may increase risk via mechanism that alters intestinal microbiota

• Pathogenesis of synovitis and joint damage
  • Inflammatory synovitis in JIA similar to synovitis in adult rheumatoid arthritis
  • Inflammation prompts pannus formation, with cartilage and bone erosions mediated by degradative enzymes, such as metalloproteinases

• Complex role of genetics
  • Role of genetic factors supported by
    • Increased prevalence of autoimmunity among first-degree relatives of patients with JIA
    • Reported monozygotic twin concordance rates (ranges from 25% – 40%)
  • Human leukocyte antigen (HLA) region (encodes major histocompatability complex) is most important genetic contributor
  • Many non-HLA regions reported to be associated with oligoarticular and rheumatoid factor (RF)-negative polyarticular JIA subtypes
  • CD80-KTELC1 and JMJD1C -genetic associations not found in other autoimmune diseases; includes genes involved in
    • T-cell development/activation
    • regulating gene …….

      Source: https://www.clinicaladvisor.com/home/stat-consult/stat-consult-polyarticular-juvenile-idiopathic-arthritis/

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