Enthesitis-related arthritis

Overview

•ERA is a subtype of juvenile idiopathic arthritis (JIA) - part of the seronegative spondyloarthropathy family

•Strong HLA-B27 association (up to 80-90%); predilection for older adolescent boys

•Closely related to adult ankylosing spondylitis spectrum

Presentation

•Arthritis - asymmetric, predominantly lower limb (knees, ankles, hips); morning stiffness improving with activity

•Enthesitis - localised tenderness at tendon/ligament insertion sites (Achilles tendon at calcaneus is classic)

•Dactylitis - diffuse 'sausage digit' swelling from combined synovitis and tenosynovitis

•Sacroiliitis - buttock/low back pain in older adolescents; indicates axial involvement

•Anterior uveitis - typically acute, painful, red eye (unlike oligoarticular JIA where uveitis is asymptomatic); asymptomatic uveitis also occurs so annual ophthalmology screening required regardless

•Inflammatory bowel disease - associated (Crohn's and UC)

•Psoriasis - psoriatic plaques, nail pitting, onycholysis

Investigations

🥇 First-line

•HLA-B27 - positive in up to 80-90%; supports diagnosis, predicts axial progression

•ESR and CRP - elevated in active disease

•RF and ANA - typically negative (seronegative); excludes other JIA subtypes

•Plain X-ray - may be normal early; later shows erosions, sacroiliitis

🥈 Second-line

•MRI sacroiliac joints - detects early sacroiliitis before X-ray changes

•Ultrasound of entheses - confirms enthesitis with increased vascularity

Differential diagnosis

ERA vs key differentials

Feature	ERA	Psoriatic arthritis	Reactive arthritis
Joints	Asymmetric lower limb; axial	Oligoarthritis incl. DIP joints; dactylitis	Large joint oligoarthritis
Key extra-articular	Enthesitis; acute uveitis; IBD	Psoriasis; nail changes; dactylitis	Urethritis/cervicitis; conjunctivitis/uveitis
Serology	HLA-B27 positive; RF/ANA negative	RF negative (seronegative)	RF negative; follows GI/GU infection
Skin	May have psoriasis	Psoriasis (may precede arthritis or follow)	None specific

🎯

Psoriatic arthritis characteristically involves DIP joints and causes dactylitis ('sausage digit'). In 15-20% of cases, arthritis appears before psoriasis. Reactive arthritis triad: 'can't see, can't pee, can't climb a tree' (uveitis/conjunctivitis + urethritis/cervicitis + arthritis).

Management

🥇 First-line

•ibuprofen (or NSAID) - cornerstone of initial management; disease-modifying potential in ERA

•Physiotherapy and occupational therapy - maintain range of movement and function

•Intra-articular corticosteroid injection - for oligoarticular flares

🥈 Second-line

•sulfasalazine - preferred DMARD in ERA; used when NSAIDs insufficient

•methotrexate or leflunomide - alternative DMARDs for peripheral joint disease

🥉 Third-line

•TNF inhibitors (etanercept, adalimumab, infliximab) - for DMARD-refractory disease; effective for peripheral and axial disease

•Uveitis: topical corticosteroids and mydriatics for acute anterior uveitis; refractory cases - systemic DMARDs or biologics

Complications and prognosis

•Untreated anterior uveitis - band keratopathy, cataracts, glaucoma, irreversible visual loss

•Progression to ankylosing spondylitis - ERA is the JIA subtype most closely linked to adult axial spondyloarthritis

•Hip involvement in childhood - increased risk of hip replacement in adulthood; important prognostic marker

📌

Annual ophthalmology surveillance is required for all ERA patients regardless of eye symptoms, as asymptomatic uveitis can cause silent visual loss.