Juvenile Idiopathic Arthritis (JIA)

SUMMARY

Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic disease of childhood, defined by chronic joint inflammation beginning before 16 years of age, with or without extra-articular involvement. It is a clinical diagnosis of exclusion, requiring arthritis in ≥ 1 joint that persists for ≥ 6 weeks after other causes (infection, malignancy) have been ruled out.

JIA is classified into five subtypes — oligoarticular, polyarticular, systemic-onset, psoriatic, and enthesitis-related — distinguished by the number and distribution of joints involved and by their extra-articular features. Regardless of subtype, every patient develops arthritis during the disease course.

The most feared, often asymptomatic, complication is chronic anterior uveitis (highest in ANA-positive oligoarticular disease). Treatment aims to control inflammation and preserve joint function, and the overall prognosis is excellent with early diagnosis and treatment.

Epidemiology & Diagnostic Criteria

Epidemiology

JIA is the most common pediatric rheumatic disease, with arthritis as its distinguishing manifestation. Mean age of onset is 1–3 years; presentation before 6 months of age is unusual. There is an overall female predominance, with two exceptions:

• Males and females are affected equally in systemic-onset JIA (F = M).
• Males predominate in late-onset HLA-B27–related (enthesitis-related) disease.

Diagnostic criteria

Diagnosis rests on history and clinical features — there is no single confirmatory test. All of the following must be met:

• Age of onset: ≤ 16 years.
• Arthritis: in ≥ 1 joint — swelling or effusion OR limitation of motion with tenderness and increased warmth.
• Duration: persistent arthritis for ≥ 6 weeks.
• Exclusion: other causes ruled out (e.g., infection, malignancy).

Active arthritis is defined by joint swelling or effusion; ultrasound can objectively confirm an effusion when the clinical examination is equivocal.

New diagnostic criteria for systemic JIA

Systemic-onset JIA has its own proposed criteria. Diagnosis requires fever of unknown origin — excluding infectious, neoplastic, autoimmune, and monogenic autoinflammatory diseases — documented daily (≥ 39 °C once daily, falling to ≤ 37 °C between fever spikes) for at least 3 consecutive days and recurring for at least 2 weeks, together with 2 major criteria or 1 major plus 2 minor criteria.

JIA Subtypes

JIA is classified by the number and distribution of joints involved together with extra-articular features. The pattern of joint involvement — and its link to iridocyclitis (anterior uveitis) — varies by subtype.

Two subtypes carry additional sub-classifications: oligoarticular disease is persistent (≤ 4 joints throughout the first 6 months and beyond) or extended (≤ 4 joints initially, then > 4 joints after 6 months), while polyarticular disease is divided by rheumatoid factor status (RF− vs the more severe RF+). See the JIA subtype clinical and laboratory feature summary for a side-by-side reference of the three major subtypes.

The oligoarticular subtype deserves special attention because its ANA-positive patients are at highest risk for chronic anterior uveitis — inflammation of the iris and ciliary body that is typically silent until vision is threatened.

In long-standing, poorly controlled disease, chronic synovial inflammation produces radiographic joint-space narrowing and erosions.

Oligoarticular JIA

• < 5 joints involved. Accounts for 50% of cases.
• Patients usually present at 1–5 years of age with a female predominance.
• A good majority (65–85%) of patients have a positive antinuclear antibody (ANA). These patients are at high risk for developing chronic uveitis (inflammation of the iris and ciliary body).
• Articular involvement may present with swelling of one or two joints, not necessarily symmetric. The most common joints involved are the knees and hips.
• Subtypes of oligoarticular JIA are recognized on the basis of the presence and timing of joint involvement:
  • Persistent oligoarthritis: patients with one to four joints involved in the first 6 months of disease who do not develop arthritis in additional joints.
  • Extended oligoarthritis: patients with one to four joints involved during the first 6 months of disease who then develop arthritis in greater than four joints.

Polyarticular JIA

• Five or more joints involved. Accounts for approximately 30–40% of cases, with systemic involvement and extra-articular features generally mild or absent.
• Affects females more frequently than males.
• Articular involvement is characterized by a symmetric polyarthritis. It typically involves both small joints (hands and feet) and large joints (knees, ankles, and hips).
• Subtypes of polyarticular JIA are based on the absence or presence of serum rheumatoid factor:
  • RF− disease: presents both early and late in childhood.
  • RF+ disease: presents in children older than 8 years. More severe than RF− disease, with a higher risk of severe arthritis and rheumatoid nodules.

Systemic-onset JIA

• Accounts for 10–15% of cases. At presentation, severe systemic symptoms may overshadow symptoms of arthritis.
• High spiking fevers (temperature > 39°C) occur most commonly in the late afternoon or evening and subsequently return quickly to baseline or subnormal levels (quotidian fever pattern).
• Transient salmon-pink macular rash is most commonly found on the trunk and proximal extremities, especially during febrile episodes. The rash is evanescent (occurs with fever spikes and then fades) and nonpruritic.
• Hepatosplenomegaly.
• Lymphadenopathy.
• Other features include:
  • Fatigue, anorexia, weight loss, and failure to thrive.
  • Serositis, including pericarditis and pleuritis.
  • CNS involvement, including meningitis and encephalopathy.
  • Myositis and tenosynovitis.

SYSTEMIC-ONSET JIA HIGHLIGHTS

Systemic-onset JIA (Still disease) accounts for 10–15% of cases and is the only subtype with an equal sex distribution (F = M). At presentation, severe systemic symptoms may overshadow the arthritis.

The hallmark features are:

• Quotidian fever: high spikes > 39 °C, most commonly in the late afternoon or evening, returning quickly to baseline or subnormal levels.
• Evanescent salmon-pink macular rash: non-pruritic, on the trunk and proximal extremities, appearing with fever spikes and then fading.
• Hepatosplenomegaly.
• Lymphadenopathy.

The most common non-specific systemic complaints are fatigue, anorexia, and weight loss. Other organ involvement may include serositis (pericarditis and pleuritis) and, less commonly, CNS involvement, myositis, and tenosynovitis.

LABORATORY FINDINGS

Laboratory results are nonspecific; when present, they reflect the presence or extent of inflammation and are most useful for evaluating other disease processes.

Serum (markers of inflammation): elevated ESR and CRP, thrombocytosis (elevated platelet count), hyperferritinemia, and hypergammaglobulinemia.

Hematology: anemia that is typically microcytic and hypochromic, consistent with anemia of chronic disease.

Rheumatoid markers:

• Rheumatoid factor (RF): negative in most patients. It is not diagnostic, but RF positivity helps determine prognosis in polyarticular disease (more severe arthritis, rheumatoid nodules).
• Antinuclear antibody (ANA): present in 65–85% of oligoarticular and ~50% of polyarticular disease, but rare in systemic-onset JIA. ANA is not a diagnostic test — it stratifies the risk of uveitis.

MANAGEMENT

The goals of treatment are to decrease joint inflammation and preserve function. Management combines pharmacologic control of inflammation with physical, surgical, and supportive measures.

• Control of inflammation: NSAIDs are first-line to reduce pain and inflammation; immunomodulatory agents — glucocorticoids, methotrexate, sulfasalazine, and TNF inhibitors — are used for more severe symptoms.
• Mechanical / physical measures: physical and occupational therapy to maintain range of motion and function.
• Surgery: joint replacement or synovectomy, generally reserved for recalcitrant joint contractures or destruction.
• Supportive: routine ophthalmologic (slit-lamp) screening for uveitis and psychosocial support.

Prognosis: the outlook is excellent with appropriate early diagnosis and treatment; the incidence of complications depends on the type and subtype of JIA. Refer to the comprehensive JIA overview (epidemiology, treatment, and complications) for a consolidated reference on management and key complications such as uveitis and bone erosion.

KEY POINTS FOR EXAMS

For a single-source review of how the three major subtypes differ at the bedside and in the lab, see the systemic vs polyarticular vs oligoarticular JIA feature summary.