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Arthritis, Juvenile Idiopathic (JIA)

Basics

  • Most common chronic pediatric rheumatologic disease.
  • Age of onset <16 years; symptoms ≥6 weeks.
  • ILAR classification (7 subtypes):
  • Systemic (10%): fever ≥2 weeks, rash, serositis, hepatosplenomegaly, lymphadenopathy.
  • Polyarticular RF-positive (2-7%): ≥5 joints, RF positive on 2 tests ≥3 months apart.
  • Polyarticular RF-negative (10-30%): ≥5 joints, RF negative.
  • Oligoarticular (30-60%): 1–4 joints; persistent and extended types.
  • Psoriatic arthritis (5%): arthritis + psoriasis or dactylitis, nail changes, or family history.
  • Enthesitis-related arthritis (1-11%): arthritis/enthesitis + sacroiliac pain, HLA-B27, uveitis, or family history.

  • Undifferentiated (11-21%): overlapping or unclassifiable.

  • Systems affected: musculoskeletal, hematologic, lymphatic, immunologic, dermatologic, ophthalmologic, GI.

Epidemiology

  • 54% of cases in children aged 0–5 years.
  • Incidence: 2–20 per 100,000 children <16 years in developed nations.
  • Prevalence: 16–150 per 100,000 children <16 years.

Etiology & Pathophysiology

  • Immunodysregulation: humoral & cellular; T lymphocytes key.
  • Genetic predisposition: IL2RA/CD25, VTCN1 loci.
  • Environmental triggers: infections (rubella, parvovirus B19), heat shock proteins, immunodeficiencies.

Risk Factors

  • Female gender (3:1 ratio).

Commonly Associated Conditions

  • Autoimmune disorders.
  • Chronic anterior uveitis (iridocyclitis).
  • Nutritional impairment.
  • Growth issues.

Diagnosis

History

  • Arthralgia, fever, fatigue, malaise, myalgias, weight loss, morning stiffness.
  • Limp if lower extremities involved.
  • Arthritis ≥6 weeks.

Physical Exam

  • Joint swelling, effusion, limited range of motion, tenderness, warmth.
  • Rash, rheumatoid nodules (rare), lymphadenopathy, hepatosplenomegaly.
  • Enthesitis, dactylitis (especially psoriatic type).

Differential Diagnosis

  • Legg-Calvé-Perthes disease, toxic synovitis, growing pains.
  • Septic arthritis, osteomyelitis, viral/mycoplasmal infections.
  • Reactive arthritis, rheumatic fever, Reiter syndrome.
  • IBD-associated arthritis.
  • Hemoglobinopathies, hemarthrosis, rickets.
  • Leukemia, bone tumors, neuroblastoma.
  • Vasculitis (IgA vasculitis), Kawasaki disease.
  • SLE, dermatomyositis, mixed connective tissue disease, sarcoidosis, systemic sclerosis.
  • Farber disease.
  • Trauma (accidental/nonaccidental).

Diagnostic Tests

  • CBC: normal/elevated leukocytes (systemic), lymphopenia, thrombocytosis, anemia.
  • LFTs, renal function (baseline).
  • Joint fluid analysis to exclude infection.
  • ESR, CRP elevated (CRP often disproportionately high).
  • Myeloid-related proteins (MRP 8/14) associated with flares.
  • ANA positive (up to 70% in oligoarticular JIA; uveitis risk).
  • RF positive (2-10%), poor prognosis.
  • HLA-B27 positive in enthesitis-related arthritis.
  • Imaging: X-rays (early soft tissue swelling, periosteal reaction, later erosions, cysts, sclerosis).
  • MRI for synovial hypertrophy and cartilage degeneration.
  • Ultrasound to assess effusions.
  • Synovial biopsy if needed.

Treatment

General Measures

  • Control active disease, minimize extra-articular complications.
  • Regular ophthalmologic exams (every 3–4 months) for ANA-positive and oligoarticular JIA (first 3 years).
  • Moist heat, splints, aerobic/weight-bearing/aquatic exercises.

Medications

  • First line (≤4 joints): NSAIDs (ibuprofen, naproxen, celecoxib); efficacy in ~50%. Monitor for adverse effects.
  • Intra-articular corticosteroids for persistent oligoarthritis or poor prognosis.
  • ≥5 joints or high disease activity: Methotrexate after 1–2 months NSAIDs failure.
  • Second line: DMARDs (methotrexate, sulfasalazine, leflunomide), TNF inhibitors (etanercept, infliximab, adalimumab).
  • Other biologics: IL-1 and IL-6 inhibitors under investigation.
  • Dosing examples: methotrexate 10 mg/m2/week PO or SC; etanercept 0.8 mg/kg SC weekly.
  • Rituximab and tocilizumab for refractory polyarticular RF-positive cases.
  • Anakinra (IL-1 antagonist) for systemic JIA with active fever.

Issues for Referral

  • Pediatric rheumatologist.
  • Orthopedics for articular complications.
  • Ophthalmology for uveitis screening.
  • Physical/occupational therapy.
  • Behavioral health support as needed.

Surgery

  • Joint replacement (hip/knee) for severe disease.
  • Soft tissue release if splinting/traction fails.
  • Limb deformity correction.
  • Synovectomy rarely performed.

Ongoing Care

Follow-Up

  • Monitoring based on disease activity and medication.
  • Labs: CBC, urinalysis, LFTs, renal function.
  • Methotrexate: monthly labs for toxicity.

Patient Education

  • Psychosocial support, school, behavioral strategies.
  • Available healthcare resources and support groups.
  • American College of Rheumatology patient resources.

Prognosis

  • 50–60% achieve remission.
  • Functional ability linked to disease control and muscle/joint maintenance.
  • Poor prognosis: active disease at 6 months, polyarticular/extended pauciarticular, female gender, RF/ANA positivity, persistent morning stiffness, erosions, hip involvement.

Complications

  • Blindness, band keratopathy, glaucoma.
  • Short stature, micrognathia (TMJ involvement).
  • Debilitating joint disease.
  • DIC, hemolytic anemia.
  • NSAID adverse effects: GI, renal, CNS.
  • DMARD toxicities: bone marrow suppression, hepatic, dermatitis.
  • TNF inhibitors: infection risk.
  • Osteoporosis, avascular necrosis.
  • Macrophage activation syndrome.

ICD10 Codes

  • M08.90 Juvenile arthritis, unspecified
  • M08.80 Other juvenile arthritis
  • M08.00 Unspecified juvenile rheumatoid arthritis

Clinical Pearls

  • Most common arthritis in children.
  • Consider in any child presenting with limp.
  • High-titer RF indicates worse prognosis.
  • DMARDs improve symptoms.
  • NSAIDs typically first-line therapy.