Reactive arthritis

Overview

Reactive arthritis (ReA) - a sterile inflammatory arthropathy triggered by a distant infection (GI or GU), occurring 1-4 weeks before joint symptoms. The joint itself is NOT infected.

Presentation

🧠

Classic triad: arthritis + urethritis + conjunctivitis - 'can't see, pee or climb a tree'. The complete triad is seen in a minority; not all three need be present simultaneously.

•Arthritis - asymmetric oligoarthritis (2-4 joints), predominantly lower limb (knees, ankles, feet); warm, swollen, tender

•Urethritis - dysuria, urethral/vaginal discharge; not active infection

•Conjunctivitis - bilateral, mild; chemosis and watery discharge

•Preceding infection - diarrhoeal illness or urogenital symptoms 1-4 weeks before joint onset; most commonly *Chlamydia trachomatis*, *Salmonella enterica*, *Campylobacter jejuni*

•Enthesitis - Achilles tendon insertion, plantar fascia

•Keratoderma blennorrhagica - hyperkeratotic lesions on soles/palms

•Circinate balanitis - painless shallow ulcerative lesions on glans penis

🚨

Uveitis (painful red eye with photophobia) is distinct from the mild painless conjunctivitis - requires urgent ophthalmology review.

Investigations

ReA is a clinical diagnosis. Investigations primarily exclude septic arthritis.

•Joint aspiration - sterile inflammatory picture: elevated WBCs, no organisms on Gram stain, no crystals (excludes septic arthritis and crystal arthropathy)

•Urethral/cervical swab or urine NAAT - identify *Chlamydia trachomatis*

•Stool culture - if recent diarrhoeal illness

•CRP/ESR - elevated in active inflammation

•Rheumatoid factor and ANA - negative (seronegative condition)

•HLA-B27 - positive in majority; supports but does not confirm diagnosis alone

⚠️

A negative Gram stain does NOT rule out septic arthritis. However, the classic triad + preceding infection + sterile inflammatory aspirate strongly supports ReA over septic arthritis.

Management

🥇 First-line

•NSAIDs (e.g. naproxen, ibuprofen) - mainstay for acute ReA; reduce joint inflammation and pain

•Treat underlying infection: if *Chlamydia trachomatis* identified, treat with doxycycline or azithromycin and refer to sexual health; antibiotic treatment of GI trigger does not reliably prevent/shorten ReA

🥈 Second-line

•intra-articular corticosteroids - if small number of joints fail to respond to NSAIDs

•oral glucocorticoids (e.g. prednisolone) - if NSAIDs insufficient and multiple joints involved

•Third-line (chronic/refractory >6 months): DMARDs - sulfasalazine or methotrexate; refer to rheumatology

💡

Most cases are self-limiting, resolving within 4-6 months. HLA-B27 positivity is associated with a more severe, prolonged course and higher risk of chronic/recurrent disease or progression to spondyloarthropathy.