Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic disease of childhood: arthritis of unknown cause that begins before age 16 and persists for at least 6 weeks, diagnosed only after infection, malignancy, and other identifiable causes of joint inflammation have been excluded.^[1] JIA is not a single disease — it is an umbrella term for 7 clinically distinct subtypes defined by the International League of Associations for Rheumatology (ILAR) classification system, and which subtype a child has genuinely changes both prognosis and treatment selection, unlike adult rheumatoid arthritis's comparatively uniform treat-to-target approach.^[1] See the platform's Rheumatoid Arthritis chapter for the shared pharmacotherapy mechanisms (methotrexate, TNF inhibitors, and the broader biologic DMARD classes) that this chapter cross-references rather than re-explains in full; the content here focuses on what is genuinely different about the pediatric disease.

Epidemiology

JIA is the most common chronic rheumatic disease of childhood. Population-based Canadian data from Manitoba show a prevalence of approximately 117 per 100,000 children and adolescents 18 years of age or younger, with an incidence that declined from 14.0 per 100,000 in 2000/2001 to 9.2 per 100,000 in 2010/2011; comparable Canadian provincial estimates are 98 per 100,000 in Saskatchewan and 80 per 100,000 in Quebec.^[2] Oligoarticular JIA is the most common subtype, typically affecting toddlers and preschool-age girls; RF-positive polyarthritis more closely mirrors adult-onset disease and tends to present in adolescent girls; systemic JIA has no sex predominance and can begin at any age throughout childhood.^[1]

The ILAR classification — the organizing framework for this entire chapter

Unlike adult RA, JIA is subdivided into 7 mutually exclusive categories based on the pattern of joint involvement in the first 6 months of disease, plus specific extra-articular features and serology. Getting the subtype right at diagnosis genuinely changes both prognosis and the treatment approach used throughout this chapter — it is not just a labelling exercise.^[1]

Clinical presentation

The hallmark is joint swelling, pain, and morning stiffness or "gelling" after periods of inactivity that improves with movement through the day — the same core pattern as adult RA. A genuinely pediatric-specific twist: young children very often cannot verbalize joint pain clearly, and may instead present with a limp, reluctance to use a limb, regression of previously acquired motor skills, or simple irritability rather than a clear complaint of pain — a presentation that is easy to miss or misattribute to a minor injury. Joint swelling is often more reliable than a pain history in this age group. Growth disturbance is a genuinely pediatric-specific complication of chronic inflammation, distinct from anything seen in adult RA: it can be localized (leg-length discrepancy from asymmetric knee involvement, or micrognathia from temporomandibular joint arthritis) or generalized (short stature from the combined effect of chronic systemic inflammation and corticosteroid exposure) — see Monitoring & Follow-Up.

• Age under 16 years at onset — required by definition; oligoarthritis peaks at ages 1-3 years, while RF-positive polyarthritis more often begins in adolescence.
• Female sex for oligoarthritis and polyarthritis (both RF-positive and RF-negative); enthesitis-related arthritis is more common in boys.
• Genetic susceptibility, including HLA associations — HLA-B27 in particular for enthesitis-related arthritis, and various HLA-DR alleles for oligoarthritis and RF-negative polyarthritis.
• ANA positivity — not a risk factor for JIA itself, but the single most important risk stratifier for silent chronic anterior uveitis once JIA is diagnosed (see Monitoring & Follow-Up).
• Family history of JIA or another autoimmune/rheumatic disease; for enthesitis-related arthritis specifically, a first-degree relative with ankylosing spondylitis, inflammatory-bowel-disease-associated arthritis, reactive arthritis, or acute anterior uveitis.
• A preceding infectious or environmental trigger in a genetically susceptible child is suspected for most subtypes, but no single causative organism or exposure has been confirmed.

JIA is a clinical diagnosis of exclusion

There is no single confirmatory test for JIA. The diagnosis requires objective arthritis (joint swelling, or at least 2 of limited range of motion, tenderness/pain on motion, and warmth) in 1 or more joints, present for at least 6 weeks, with onset before age 16 — made only after excluding infection, malignancy, and other identifiable causes of childhood joint inflammation.^[1]

Key differential diagnoses

Investigations

• ESR and CRP — support the diagnosis and help track disease activity, but a normal result does not exclude JIA, particularly oligoarthritis.
• ANA — not diagnostic of JIA itself, but the single most important test for uveitis risk stratification once JIA is confirmed (see Monitoring & Follow-Up).
• Rheumatoid factor and anti-CCP — define the RF-positive polyarthritis subtype; anti-CCP supports RF-positive disease and, like adult seropositive RA, associates with more erosive disease.
• HLA-B27 — supports (but is not required for) the enthesitis-related arthritis classification.
• CBC with differential/blood film, and LDH — screen for leukemia and other malignancy before starting any corticosteroid, since corticosteroids can transiently improve leukemic bone/joint pain and delay the correct diagnosis.
• Plain radiographs at baseline for the affected joint(s); MRI is increasingly used to detect subclinical synovitis and is particularly useful for the temporomandibular joint and sacroiliac joints (enthesitis-related arthritis) where clinical exam is less reliable.

• Achieve inactive disease or clinical remission, tracked with a validated composite disease-activity measure (e.g., the Juvenile Arthritis Disease Activity Score, JADAS) rather than symptoms alone.
• Treat early and adjust promptly against the defined target — a treat-to-target philosophy that genuinely parallels adult RA's own approach, applied here with pediatric-specific dosing and monitoring.
• Preserve joint function, and protect normal growth and pubertal development from the effects of both chronic inflammation and corticosteroid exposure.
• Prevent long-term joint damage, including growth disturbance (leg-length discrepancy, micrognathia) specific to a still-growing skeleton.
• Prevent the sight-threatening complications of JIA-associated uveitis through scheduled screening, not symptom-triggered care.
• Recognize and urgently treat macrophage activation syndrome in systemic JIA before it becomes life-threatening.
• Support a successful, well-planned transition to adult rheumatology care, since many JIA patients continue to have active disease into adulthood.

• Multidisciplinary team care — pediatric rheumatology, ophthalmology, physical and occupational therapy, and, where growth or nutrition is affected, pediatric endocrinology and dietetics — improves outcomes beyond medication alone.^[7]
• Regular physical activity is safe, beneficial, and belongs in every treatment plan — encourage normal participation in play, sport, and physical education rather than restricting activity because of joint disease, matching the same principle established for adult RA.
• Physical and occupational therapy for joint protection, range-of-motion preservation, and muscle strengthening around affected joints; splinting where indicated.
• School accommodations as needed — extra time between classes for joint stiffness, modified physical education, and staff awareness of the medication and monitoring schedule.
• Nutrition support and monitoring for a child with growth disturbance or on long-term corticosteroid therapy (see Monitoring & Follow-Up).
• Psychological support — chronic illness, visible joint changes, and a demanding treatment/monitoring schedule all carry a real psychosocial burden for the child and family.
• Caregiver and patient education — proactively explain that uveitis screening continues on schedule even when the joints are doing well and the eyes look and feel normal, since most JIA-associated uveitis is silent; this is one of the most common points of family confusion and missed follow-up.^[4]
• For families of a child with systemic JIA, explicit education on the warning signs of macrophage activation syndrome (persistent high fever, new bruising/bleeding, lethargy) and to seek urgent care rather than waiting it out.

Macrophage activation syndrome — a life-threatening emergency in systemic JIA

Recognizing MAS

• Persistent high fever that may lose the typical quotidian (spiking-and-resolving) pattern of systemic JIA, instead becoming sustained.
• Hepatosplenomegaly, lymphadenopathy, and a purpuric or hemorrhagic rash (distinct from the evanescent salmon-pink rash of uncomplicated systemic JIA).
• CNS dysfunction (irritability, lethargy, seizure) and multiorgan involvement in severe cases.
• A falling platelet count in a patient whose systemic JIA had previously caused thrombocytosis is a genuinely important early clue, even when the platelet count is still technically within the normal range for age — a relative drop matters.
• A falling ESR with a rising or persistently high CRP — a classic and easily missed dissociation, caused by hypofibrinogenemia from disseminated intravascular coagulation artificially lowering the ESR. A "better-looking" ESR in a sicker-looking child is a red flag, not reassurance.

2016 EULAR/ACR/PRINTO classification criteria

In a febrile patient with known or suspected systemic JIA, MAS is classified by ferritin above 684 ng/mL (μg/L) plus at least 2 of the following 4 laboratory criteria: platelet count 181 × 10⁹/L or below; AST above 48 U/L; triglycerides above 156 mg/dL (1.76 mmol/L); or fibrinogen 360 mg/dL or below.^[3] This is a classification tool intended for research case definition and is presented here as a teaching reference rather than an interactive calculator — clinical suspicion and urgent treatment should never wait for a complete criteria set to be confirmed.

Treatment — urgent, do not wait

Confirmed or strongly suspected MAS is treated as an emergency: IV pulse methylprednisolone plus an IL-1 inhibitor (anakinra, preferred for its short half-life and rapid titratability in a critically ill child) started together, with cyclosporine added as a steroid-sparing second agent for disease not rapidly responding to corticosteroid and anakinra alone. Supportive, often ICU-level, care is needed for multiorgan dysfunction.^[3] See Drug Tables for dosing.

Transition to adult rheumatology care

Many JIA patients continue to have active disease into adulthood, making a well-planned transition genuinely important rather than a formality. Canadian CAPRI registry data show that at the final pediatric rheumatology visit around age 17, roughly one-third of patients (32%) still had active disease, 26% had clinically detected joint damage, 14% had a history of uveitis, and about three-quarters remained on medication (31% on a biologic DMARD).^[8] Begin transition planning well before the actual transfer — confirm the adult rheumatology team has full records, including uveitis history and any joint damage, and do not assume disease control achieved in childhood will be self-evident to the new adult-care team without an explicit handoff.

Temporomandibular joint (TMJ) arthritis

TMJ involvement can be clinically silent while still causing progressive micrognathia and facial growth asymmetry in a growing child — a specific reason for a low threshold to image the TMJ (MRI) in a child with any JIA subtype, not only when jaw symptoms are reported. TMJ arthritis is also a specific anesthesia consideration: reduced jaw opening can complicate airway management and should be flagged before any procedure requiring intubation.^[5]

Adolescents and reproductive planning

Discuss contraception and family planning with any adolescent of reproductive potential started on methotrexate or leflunomide, using the same preconception principles described in the Rheumatoid Arthritis chapter's Special Populations section (methotrexate discontinuation at least 3 months before attempting conception; leflunomide's washout protocol) — these do not change for a pediatric/adolescent patient once conception becomes a realistic possibility.

Uveitis screening — one of the most important management points in this chapter

Most JIA-associated chronic anterior uveitis is entirely asymptomatic until damage has already occurred, which is exactly why screening is scheduled and risk-based rather than triggered by eye symptoms.^[9] Every child with JIA needs a baseline slit-lamp ophthalmologic exam within 1-3 months of diagnosis, regardless of eye symptoms, followed by ongoing screening at a frequency determined by subtype, ANA status, age at onset, and disease duration.^[4]

The Canadian Rheumatology Association's adaptation of this schedule specifies at least every 3 months for the first 4 years in the highest-risk group.^[4] Screening continues for as long as meaningful risk persists — do not stop simply because the joints have been quiet for a period, since uveitis risk and joint disease activity do not track together.

Uveitis treatment threshold — a genuinely Canadian-specific adaptation

Topical prednisolone acetate 1% is first-line for active uveitis. The Canadian Rheumatology Association adapted the American College of Rheumatology's original threshold for adding systemic therapy — moving from needing more than 1-2 drops per day to needing more than 2 drops per day for 3 months or longer before escalating — reflecting Canadian-context shared decision-making about when topical therapy alone remains reasonable.^[4] When systemic therapy for uveitis is needed, methotrexate is 1st-line, with adalimumab or infliximab preferred over etanercept specifically because etanercept is less effective for uveitis control despite being an entirely reasonable choice for joint disease alone.^[9]

Growth and bone health monitoring — genuinely pediatric-specific

Chronic inflammation and corticosteroid exposure both impair growth independently, and their combined effect in an undertreated or long-term-corticosteroid-dependent child is a real, measurable risk distinct from anything in adult RA management.^[1] Measure height, weight, and pubertal staging at every visit and plot on an age-appropriate growth curve; a child falling off their growth curve needs both treatment escalation (to control the underlying inflammation) and, where corticosteroid exposure is significant, specialist-directed evaluation for growth hormone therapy. Catch-up growth is genuinely possible once disease is controlled and corticosteroid exposure is minimized, so growth monitoring should continue for as long as active treatment continues, not just at diagnosis. Bone health monitoring (calcium and vitamin D intake, weight-bearing activity, and bone density assessment where corticosteroid exposure is prolonged or fracture risk is otherwise elevated) follows the same general principles as the Rheumatoid Arthritis chapter's corticosteroid-induced-osteoporosis content, adapted to pediatric dosing (see Drug Tables).

Disease activity measurement

The Juvenile Arthritis Disease Activity Score (JADAS) is the most widely used composite measure, combining an active joint count, physician and parent/patient global assessment, and ESR or CRP — analogous in concept to the DAS28 used in adult RA. Like the DAS28, it requires a hands-on joint examination and is a specialist-administered tool, presented here as reference only rather than a self-service calculator.

Drug monitoring

Methotrexate and biologic/tsDMARD pre-therapy and ongoing laboratory monitoring (CBC, LFTs, tuberculosis and hepatitis B/C screening before starting a biologic) follow the same principles detailed in the Rheumatoid Arthritis chapter's own Monitoring & Follow-Up section — apply them here with pediatric dosing and age-appropriate vaccination schedules. Live vaccines are avoided during biologic/tsDMARD therapy; inactivated vaccines remain recommended on schedule.^[10]

1. Confirm the correct ILAR subtype classification was applied — an incorrect subtype assignment can lead to a mismatched treatment approach; reassess if the clinical picture has evolved (e.g., oligoarthritis extending beyond 4 joints after 6 months reclassifies the treatment approach even though the ILAR category name does not formally change).
2. Confirm adherence and correct administration technique before declaring treatment failure — a common, reversible cause of apparent nonresponse, particularly for weekly oral/SC methotrexate in a child who dislikes injections or has needle anxiety.
3. Oligoarthritis: if a joint recurs after intra-articular corticosteroid injection, or more than 4 joints become involved after the first 6 months (extended oligoarthritis), add methotrexate rather than repeating injections indefinitely.
4. Polyarthritis: if inadequate response to methotrexate at an adequate dose and duration (3 months), add a TNF inhibitor; if inadequate response to a first TNF inhibitor, switch to a biologic with a different mechanism (abatacept, tocilizumab) rather than cycling to a second TNF inhibitor, mirroring the same principle as adult RA.
5. Systemic JIA: if inadequate response to an IL-1 inhibitor, switching to an IL-6 inhibitor (or vice versa) is reasonable — response to individual agents within this class is variable and no single preferred first agent is established; escalate corticosteroid bridging in the interim if systemic features are significant.
6. Persistent or recurrent fever, cytopenia, or clinical deterioration in a patient with systemic JIA at any point in this pathway: reassess urgently for macrophage activation syndrome rather than simply escalating the current regimen (see Special Populations).
7. Progressive joint damage, growth disturbance, or new organ involvement despite an apparently adequate regimen: reconfirm the diagnosis and reconsider an alternative or overlapping diagnosis before further escalating an unchanged treatment approach.

• Waiting for a child to report joint pain clearly before investigating — young children often present with a limp, reluctance to use a limb, or simple irritability instead.
• Treating oligoarthritis with NSAID monotherapy alone as if it were adequate disease control, rather than proceeding to intra-articular corticosteroid injection as genuine 1st-line therapy.
• Stopping or spacing out uveitis screening once the joints are well controlled — joint disease activity and uveitis risk do not track together, and most uveitis is silent until damage occurs.
• Waiting for eye symptoms before referring for ophthalmologic assessment in a child with oligoarthritis or RF-negative polyarthritis — the entire point of scheduled screening is that symptoms come too late.
• Choosing etanercept over adalimumab or infliximab specifically when uveitis is present — etanercept is less effective for uveitis control even though it remains a reasonable choice for joint disease alone.
• Missing early macrophage activation syndrome because the fever pattern looks reassuringly different from a typical systemic JIA flare, or because a falling ESR is misread as clinical improvement rather than recognized as a possible sign of consumptive hypofibrinogenemia.
• Starting a corticosteroid before excluding leukemia in a child with new joint pain, bone pain, or cytopenia — corticosteroids can transiently mask malignant disease and delay the correct diagnosis.
• Overlooking growth and pubertal staging at routine visits — growth disturbance is a genuinely pediatric-specific complication that is easy to miss without deliberately plotting a growth curve at every visit.
• Failing to plan the transition to adult rheumatology care early — many patients still have active disease and are on biologic therapy at the point of transfer, and an unplanned handoff risks a genuine gap in care.
• Treating an established biologic-class response principle from adult RA (e.g., switching mechanism rather than cycling within class after inadequate response) as though it does not apply in pediatrics — the same principle holds, adapted to pediatric dosing.

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

NSAIDs — Symptom Control

Adjunctive symptom control across all subtypes; not disease-modifying and not sufficient as monotherapy for confirmed JIA.

Intra-Articular Corticosteroid

1st-line therapy for oligoarthritis, and an adjunct for a flared joint in any subtype.

Conventional Synthetic DMARDs

Methotrexate is the pediatric csDMARD backbone; dosing, folic acid co-administration, and monitoring principles mirror the Rheumatoid Arthritis chapter's methotrexate content, adapted to body-surface-area dosing.

Tumor Necrosis Factor (TNF) Inhibitors

Adalimumab and infliximab are preferred over etanercept specifically when JIA-associated uveitis is present, since etanercept is less effective for uveitis control. Complete tuberculosis and hepatitis B/C screening before starting, as detailed in the Rheumatoid Arthritis chapter.

Other Biologic DMARDs

Alternatives for polyarthritis after TNF-inhibitor failure, or when a different mechanism of action is preferred.

Interleukin-1 (IL-1) Inhibitors — Systemic JIA and MAS

Target the distinct autoinflammatory pathophysiology of systemic JIA; anakinra's short half-life makes it the preferred agent when rapid dose titration may be needed.

Systemic Corticosteroids

Route and dose scale with acuity; use the lowest effective dose for the shortest duration given the direct, measurable effect of corticosteroid exposure on growth in a still-growing child.

Macrophage Activation Syndrome — Refractory Adjunct

Reserved for MAS not rapidly responding to IV pulse corticosteroid plus an IL-1 inhibitor.

Bone Health Support

For a child with prolonged corticosteroid exposure or otherwise elevated fracture risk, adapted from the Rheumatoid Arthritis chapter's corticosteroid-induced-osteoporosis principles to pediatric intake targets.