Psoriatic Juvenile Idiopathic Arthritis

Psoriatic juvenile idiopathic arthritis (PsJIA) is a subtype of juvenile idiopathic arthritis (JIA) characterised by the co-occurrence of arthritis and psoriasis, or arthritis with at least two of the following: dactylitis, nail pitting, or a first-degree relative with psoriasis. It is a chronic inflammatory arthropathy affecting children and adolescents, with onset before age 16 years. PsJIA accounts for approximately 6–8% of all JIA cases in Australia.

Epidemiology and Clinical Subtypes

• Prevalence: PsJIA affects approximately 2–4 per 100,000 children in Australia; peak onset is bimodal — early childhood (2–4 years) and late childhood/adolescence (9–11 years)
• Sex distribution: Overall female predominance in early-onset; more equal sex ratio in later onset
• Oligoarticular PsJIA: ≤4 joints affected in the first 6 months; frequently involves knee, ankle, or small joints of the hands/feet
• Polyarticular PsJIA: ≥5 joints affected; typically RF-negative; may involve DIP joints (unusual in other JIA subtypes)
• Dactylitis: 'Sausage digit' — diffuse swelling of an entire finger or toe due to combined flexor tenosynovitis and joint inflammation; highly characteristic of PsJIA
• Associated uveitis: Chronic anterior uveitis occurs in approximately 15–20% of PsJIA patients — often asymptomatic and potentially sight-threatening if untreated

PsJIA is associated with significant morbidity including joint damage, growth disturbance, and ocular complications. Biological therapies, particularly TNF inhibitors, have substantially improved outcomes over the past two decades. Management requires a multidisciplinary approach coordinated between paediatric rheumatology, ophthalmology, dermatology, and allied health.

PsJIA shares immunopathological features with adult psoriatic arthritis (PsA) and other JIA subtypes but has distinct characteristics reflecting the developing immune and musculoskeletal system.

Immune Dysregulation

• T-cell driven inflammation: Th1 and Th17 pathways are central — IL-17, IL-22, and TNF-α drive both synovial and skin inflammation
• IL-23/IL-17 axis: Particularly important in enthesitis and dactylitis; IL-23 promotes Th17 differentiation at entheseal sites
• TNF-α: Key mediator of synovitis, osteoclast activation, and joint destruction in PsJIA
• Type I interferons: Elevated in some PsJIA patients — may contribute to the skin and joint phenotype
• Genetic factors: HLA-C*06:02 associated with psoriasis; HLA-B27 less commonly positive than in enthesitis-related JIA but may occur in PsJIA with enthesitis

Enthesitis and Dactylitis

Enthesitis (inflammation at tendon/ligament bone insertions) is a defining feature of the spondyloarthritis spectrum to which PsJIA belongs. Dactylitis results from a combination of flexor tenosynovitis, enthesitis, and joint inflammation within a digit. The IL-17/IL-23 axis is particularly important at entheseal sites, where mechanical stress and microbial signals trigger innate immune activation.

Genetic Associations

PsJIA has a heterogeneous presentation. The combination of arthritis with psoriatic features distinguishes it from other JIA subtypes. Recognition of dactylitis, enthesitis, and nail changes alongside arthritis is essential for early diagnosis.

Articular Features

• Oligoarthritis: Asymmetric joint involvement; commonly knee, ankle, wrist, and small joints of hands/feet
• DIP joint involvement: Distal interphalangeal joint arthritis is characteristic of PsJIA (unusual in other JIA subtypes) — often associated with nail changes in the same ray
• Dactylitis: Diffuse swelling of entire finger or toe ('sausage digit'); may precede or accompany joint involvement; indicates tendon sheath inflammation
• Enthesitis: Pain and tenderness at insertion sites — common sites include Achilles tendon, plantar fascia, tibial tubercle, and patella
• Sacroiliitis: Less common in PsJIA than in enthesitis-related JIA but may occur, particularly in HLA-B27–positive older patients

Dermatological and Nail Features

• Psoriatic skin disease: Plaque psoriasis, guttate psoriasis, scalp psoriasis, or inverse psoriasis — may precede, follow, or occur simultaneously with arthritis
• Nail pitting: Multiple small pits on nail surface; highly associated with DIP arthritis and PsJIA
• Onycholysis: Separation of nail plate from nail bed — occurs in active psoriatic nail disease
• Subungual hyperkeratosis: Thickening under nail plate; associated with PsJIA activity
• Skin and nail disease severity does NOT parallel arthritis activity — they can fluctuate independently

Ocular Features

Systemic Features

• Fever is uncommon in PsJIA (unlike systemic JIA) — persistent fever should prompt reassessment
• Growth disturbance: chronic inflammation and corticosteroid use can impair linear growth
• Osteoporosis: chronic inflammation and steroid use increase fracture risk
• Fatigue and school absence are common — psychosocial assessment is important

No single investigation confirms PsJIA. Diagnosis is clinical based on ILAR criteria. Investigations serve to support the diagnosis, exclude differentials, assess disease severity, and screen for complications.

• Essential
  FBC, ESR, CRP

  Assess systemic inflammation. ESR/CRP may be normal or elevated — normal values do not exclude active PsJIA. Anaemia of chronic disease may be present in active polyarticular disease.
• Essential
  ANA (Antinuclear Antibody)

  ANA positivity occurs in approximately 50% of PsJIA and is associated with higher uveitis risk. Does not confirm diagnosis. Essential for uveitis risk stratification and screening frequency.
• Recommended
  RF (Rheumatoid Factor)

  Should be NEGATIVE in PsJIA by ILAR definition. RF positivity should prompt reclassification as RF-positive polyarticular JIA. Anti-CCP antibody may be considered if seronegative RA is in the differential.
• Recommended
  HLA-B27

  Not diagnostic for PsJIA but relevant if enthesitis or sacroiliitis present — may suggest overlap with enthesitis-related JIA. Relevant for uveitis risk assessment.
• Essential
  Joint Ultrasound

  Sensitive for synovitis, tenosynovitis, and enthesitis not detectable on examination. Useful for guiding corticosteroid injection. Power Doppler confirms active inflammation. Preferred first-line imaging in children.
• Recommended
  MRI Affected Joints/Spine

  Gold standard for early synovitis, bone marrow oedema, and sacroiliitis detection. Required if axial involvement suspected (sacroiliac MRI). Avoids radiation exposure important in children.
• Recommended
  Plain X-Ray Affected Joints

  Limited sensitivity for early disease. Useful to detect established erosions, joint space narrowing, and growth plate changes in chronic disease. Baseline X-ray of hands/feet/affected joints in polyarticular PsJIA.
• Recommended
  Slit-Lamp Examination (Ophthalmology)

  Mandatory for all PsJIA patients. Screening frequency per AAP 2019 schedule: every 3–12 months depending on age, ANA status, disease duration. Detects anterior uveitis before visual symptoms develop.
• Recommended
  DEXA Scan (when indicated)

  Consider if prolonged systemic corticosteroid use or radiological concern for osteoporosis. Assess bone mineral density; optimise calcium, vitamin D, and consider bisphosphonate if fracture risk significant.

PsJIA disease activity is assessed using validated composite measures. Treat-to-target (T2T) strategies aim for clinical inactive disease (CID) or low disease activity as defined by standardised criteria.

Validated Assessment Tools

• JADAS-10 (Juvenile Arthritis Disease Activity Score): Composite of physician global, parent/patient global, joint count (10 joints), and ESR — most widely used in PsJIA clinical trials
• cJADAS (clinical JADAS): JADAS without ESR — practical for clinical use; correlates well with JADAS-10
• CHAQ (Childhood Health Assessment Questionnaire): Functional disability score 0–3; normal ≤0.13; important for monitoring functional outcomes
• PGA (Physician Global Assessment): 0–10 VAS; component of JADAS-10
• ASDAS (Ankylosing Spondylitis Disease Activity Score): Used if axial/enthesitis-predominant disease

Uveitis Activity

• Uveitis activity is graded separately using SUN (Standardised Uveitis Nomenclature) criteria: flare (2+ step increase in cell grade), worsening, improving, or inactive
• Inactive uveitis: anterior chamber cell grade <0.5+ on two consecutive visits ≥3 months apart
• Uveitis flare may occur during JIA remission — screening must continue regardless of arthritis activity

Treatment follows a stepwise approach based on disease activity, number of joints involved, presence of enthesitis/dactylitis, uveitis, and skin disease severity. Biological DMARDs are indicated early in severe or refractory disease.

Step 1 — NSAIDs and Intra-articular Corticosteroids

Step 2 — Conventional Synthetic DMARDs

Step 3 — Biological DMARDs

JIA-associated uveitis and skin psoriasis require disease-specific management coordinated with ophthalmology and dermatology respectively. These manifestations may persist or worsen independently of joint disease.

JIA-Associated Uveitis — Treatment Pathway

Skin Psoriasis Management

• Topical therapy (mild skin disease): Moderate-potency corticosteroid ointments (mometasone, betamethasone valerate) for plaques; tar preparations or calcipotriol for maintenance; salicylic acid shampoo for scalp psoriasis
• Phototherapy (UVB): Narrowband UVB for widespread plaque psoriasis not responding to topicals — requires dermatology referral; concerns about long-term UV exposure in children
• Systemic therapy: Methotrexate is effective for both skin and joint disease; apremilast (PDE4 inhibitor) approved for adult PsA with skin disease but limited paediatric data
• Biologicals for skin: TNF inhibitors (adalimumab, etanercept) and IL-17 inhibitors (secukinumab) are effective for psoriasis; IL-17 inhibitors particularly effective for plaque psoriasis; ustekinumab (IL-12/23) used in adolescents
• Avoid photosensitising medications: Naproxen pseudoporphyria — switch NSAID if photosensitive blistering occurs

Multidisciplinary non-pharmacological management is essential for optimal outcomes in PsJIA, addressing functional, educational, and psychosocial needs of the child and family.

Physiotherapy

• Active range-of-motion exercises: Preserve joint mobility and prevent contracture — particularly important for wrist, ankle, and hip joints
• Strengthening exercises: Quadriceps, hip abductor, and periscapular strengthening to support joint stability
• Hydrotherapy: Warm water exercise — reduces pain, improves mobility, well tolerated in children with active joint disease
• Splinting: Resting splints for wrist/hand during flares to prevent contracture; functional splints for daily activities
• Exercise prescription: Regular low-impact aerobic activity (swimming, cycling) — does not worsen joint disease and improves fitness, bone density, and mood

Occupational Therapy

• Joint protection strategies and adaptive equipment for school and home
• Fine motor assessment and intervention for hand/wrist involvement
• School liaison: school participation plan, rest facilities, adapted PE, written notes in lieu of extended writing if hand pain present
• Assistive devices: pen grips, jar openers, adapted keyboard/mouse for significant hand involvement

Psychosocial Support

• Chronic disease in childhood impacts self-esteem, peer relationships, school participation, and family dynamics
• Psychological assessment for anxiety, depression, and adjustment difficulties — common in chronic paediatric disease
• Disease education for child (age-appropriate) and family — promotes adherence and self-management
• Peer support programs and JIA patient organisations (Arthritis Australia JIA resources)
• Transition planning: structured transition to adult rheumatology from approximately 14–16 years

Immunisations

Regular monitoring in PsJIA is essential to assess disease activity, medication toxicity, and complications. Frequency is guided by disease severity and treatment regimen.

Methotrexate Monitoring

Ophthalmology Screening Schedule (AAP 2019)

• ANA-positive, oligoarticular/psoriatic JIA, age <7 at onset: Every 3 months for 4 years, then every 6 months for 3 years, then annually
• ANA-negative, oligoarticular/psoriatic JIA: Every 6 months for 4 years, then annually
• Polyarticular RF-negative, age <7: Every 6 months for 4 years, then annually
• Screening frequency may be adjusted by ophthalmologist based on individual risk and clinical course

Several patient groups within PsJIA require specific management considerations.

🧒 Young Children (<6 Years)

• Dactylitis and DIP joint involvement may be the only early signs — high index of suspicion required
• Intra-articular corticosteroid under general anaesthesia is appropriate for young children with significant joint swelling
• ANA-positive young girls with oligoarticular PsJIA have the highest uveitis risk — intensive ophthalmology screening essential
• Developmental impact: assess fine motor development, gait, and school readiness
• Parent education is paramount — young children cannot self-report symptoms accurately

🧑 Adolescents

• Adherence is a major challenge in adolescence — simplify regimen where possible; SC auto-injectors improve adherence
• Body image concerns: psoriatic skin disease has significant psychosocial impact during adolescence
• Contraception counselling for females on methotrexate or leflunomide — both are teratogenic
• Smoking cessation: smoking worsens psoriasis and may reduce biological efficacy
• Transition to adult rheumatology: structured handover from approximately 16–18 years; risk of disease flare during transition

🤰 Females of Reproductive Age

• Methotrexate and leflunomide are absolutely contraindicated in pregnancy
• TNF inhibitors: etanercept and adalimumab are relatively safe in early pregnancy — discuss risk/benefit with rheumatologist; certolizumab is preferred in pregnancy (no placental transfer)
• Pregnancy should be planned with prior disease assessment and medication adjustment
• JIA often improves during pregnancy but may flare postpartum

👁️ PsJIA with Sight-Threatening Uveitis

• Topical corticosteroid frequency guided by ophthalmologist only — excessive use causes cataract and glaucoma
• Adalimumab is TGA-approved for JIA-associated uveitis — initiate promptly if uveitis fails topical therapy plus methotrexate
• Regular monitoring for complications: posterior synechiae, elevated IOP, cataract, band keratopathy
• Surgical management (cataract extraction, trabeculectomy) for uveitis complications — coordinate with ophthalmology

Stewardship in PsJIA focuses on appropriate use of biological DMARDs, avoiding unnecessary imaging, and preventing over-reliance on systemic corticosteroids in growing children.

Biological DMARD Stewardship

• PBS Authority is required for biological DMARDs in JIA in Australia — must be initiated and maintained by paediatric rheumatologist
• Response assessment at 12 weeks — if inadequate response (not achieving low disease activity), review adherence, immunogenicity, and consider alternative biological
• Anti-drug antibody testing may explain secondary failure to TNF inhibitors — consider switching within or between classes
• TNF inhibitors and uveitis: etanercept is LESS effective than adalimumab for JIA uveitis — do not substitute for uveitis management
• IL-17 inhibitors and uveitis: secukinumab may worsen inflammatory bowel disease and has limited uveitis data — caution in PsJIA with uveitis

Methotrexate Stewardship

• Subcutaneous administration preferred over oral for doses >10 mg/week — better bioavailability and fewer GI side effects
• Folate supplementation (folic acid 5 mg/week, not on MTX day) reduces mucosal and haematological toxicity without reducing efficacy
• Alcohol must be avoided in adolescents on MTX — hepatotoxicity risk
• MTX dose based on BSA (body surface area) in children — recalculate as child grows

Imaging Stewardship

• X-ray exposes growing children to ionising radiation — use ultrasound as first-line imaging for synovitis, tenosynovitis, and enthesitis
• MRI preferred over CT for sacroiliac joint assessment — no radiation and superior soft tissue resolution
• Routine repeat imaging not required in stable disease — reserve for clinical change or treatment decision

Long-term follow-up in PsJIA aims to achieve and maintain clinical inactive disease, prevent organ damage (particularly ocular), optimise growth and development, and support successful transition to adult care.

Transition to Adult Care

• Structured transition: Not a single handover event — begin education and planning from age 14; formal transition at 16–18 years depending on maturity and disease complexity
• Adult rheumatology services: PsJIA may continue as psoriatic arthritis (PsA) in adulthood; adult biologics PBS criteria differ from paediatric — plan ahead to avoid gaps in therapy
• Transfer of care documentation: Comprehensive letter to adult rheumatologist including diagnosis, previous treatments, current medications, uveitis history, and complication history
• Continuation of ophthalmology: JIA-associated uveitis may continue into adulthood — ophthalmology follow-up must continue after transition
• Reproductive planning: For females: contraception counselling before transition; for all adolescents: discuss impact of PsJIA on future fertility (rare, but disease activity affects outcomes)

Disease Course and Prognosis

• PsJIA has a variable course — approximately 30–50% achieve sustained remission off medication in adulthood
• Polyarticular and RF-negative polyarticular courses have worse structural prognosis than oligoarticular
• Persistent uveitis is the most important predictor of visual morbidity — early and consistent treatment reduces risk
• Regular exercise, healthy weight, and non-smoking are the most important modifiable lifestyle factors

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