Psoriatic juvenile idiopathic arthritis
Overview
•One of seven ILAR JIA subtypes - accounts for ~5-8% of all JIA cases
•Defined by arthritis + psoriasis, OR arthritis + characteristic extra-articular features when psoriasis is absent
•Bimodal age distribution: early peak 2-3 years (girls, oligoarticular); later peak mid-childhood to adolescence (equal sex, polyarticular)
•Joint disease commonly precedes psoriasis by months to years - do not exclude diagnosis on absence of skin plaques alone
Presentation
•Arthritis - asymmetric oligo- or polyarthritis; small finger/toe joints commonly affected; DIP involvement is distinctive (unlike RF-positive polyarticular JIA which spares DIP)
•Dactylitis - diffuse 'sausage digit' swelling caused by combined tenosynovitis and periarticular oedema; hallmark feature
•Nail pitting - punctate depressions from defective proximal nail matrix keratinisation
•Onycholysis - distal nail separation from nail bed, often yellowish
•Psoriatic plaques - check scalp, umbilicus, natal cleft, behind ears
•Enthesitis - Achilles tendon insertion, plantar fascia origin, around patella
•Uveitis - may present as acute symptomatic red eye with pain and photophobia (unlike oligoarticular JIA where uveitis is chronic and asymptomatic)
Investigations
🥇 First-line
•FBC, ESR, CRP - markers of active inflammation
•RF - expected negative; positivity suggests alternative subtype
•ANA - can be positive; positivity increases uveitis risk and influences screening frequency
•Plain X-ray - soft tissue swelling early; later asymmetric erosions at DIP/PIP, periostitis
•Slit-lamp ophthalmology - uveitis screening essential even without eye symptoms
🥈 Second-line
•MRI or ultrasound - more sensitive for early synovitis, tenosynovitis, enthesitis, sacroiliac involvement
Management
•First-line (mild disease): ibuprofen or naproxen (NSAIDs) - symptom relief only, do not alter disease course
•First-line (oligoarticular): intra-articular corticosteroid injection - targeted local effect, avoids systemic steroid side effects
🥇 First-line
•ophthalmology referral - all children require regular slit-lamp examination regardless of symptoms
•physiotherapy and occupational therapy - maintain range of motion and function
•Second-line (moderate-severe/polyarticular): methotrexate (DMARD) - first-choice DMARD; addresses both joint and skin disease; given weekly with folic acid
•Second-line (alternatives): sulfasalazine or leflunomide - if methotrexate not tolerated
•Third-line (refractory): TNF inhibitors - etanercept, adalimumab, or infliximab - for disease failing DMARD therapy; effective for joints and skin
Complications
•Chronic uveitis - cataracts, glaucoma, visual loss if undetected; regular screening non-negotiable
•Progressive joint damage - erosive arthritis, DIP bony ankylosis, loss of hand function
•Hip involvement - increased risk of hip replacement in adulthood
•Growth disturbance - localised around inflamed joints; systemic inflammation may impair linear growth
Prognosis
•~40% have ongoing active disease at 7-year follow-up
•Polyarticular onset associated with higher likelihood of chronic disease
ILAR Diagnostic Criteria
Arthritis AND psoriasis, OR arthritis PLUS at least two of the following three minor criteria:
•Dactylitis (current or past)
•Nail pitting or onycholysis
•First-degree relative with psoriasis (confirmed by dermatologist)
•Exclusion criteria: positive RF on two occasions, systemic JIA, HLA-B27-associated disease in a boy >6 years, or another JIA subtype