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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Sterile inflammatory arthritis 1–4 weeks AFTER GI infection (Campylobacter, Salmonella, Shigella, Yersinia) or urogenital infection (Chlamydia)
- Classic triad (Reiter syndrome — outdated term): arthritis + urethritis + conjunctivitis. Full triad present in minority
- Typically asymmetric oligoarthritis affecting large joints of lower limbs (knee, ankle)
- HLA-B27 positive in ~50–80% — part of the spondyloarthritis family
- Treatment: NSAIDs (first-line), intra-articular steroids, DMARDs (sulfasalazine/methotrexate) if persistent
Overview
Reactive arthritis (ReA) is a form of spondyloarthropathy characterised by sterile joint inflammation triggered by a preceding infection at a distant site. The term replaces the older eponym "Reiter syndrome." Joints are not directly infected — the inflammatory response is immune-mediated (molecular mimicry between bacterial antigens and host tissue). Common triggers include GI infections (Campylobacter, Salmonella, Shigella, Yersinia) and urogenital infections (Chlamydia trachomatis — most common in sexually acquired ReA). ReA is self-limiting in ~80% within 6–12 months but ~20% develop chronic arthritis.
Epidemiology
Incidence is approximately 30–40 per 100,000 following enteric infection and ~5 per 100,000 following urogenital infection. It predominantly affects young adults aged 20–40 years. Male predominance in sexually acquired ReA; equal sex distribution in post-enteric ReA. HLA-B27 is positive in ~50–80% and confers a worse prognosis (higher risk of chronicity and axial involvement).
Clinical Features
Symptoms
Preceding GI illness (diarrhoea) or urogenital infection (urethritis) 1–4 weeks before joint symptoms
Asymmetric oligoarthritis: large joints of lower limbs (knee, ankle) — typically acute and painful
Dactylitis: "sausage digit" — diffuse swelling of entire finger or toe
Enthesitis: pain at tendon insertions (Achilles tendinitis, plantar fasciitis)
Low back pain (sacroiliitis — axial involvement)
Conjunctivitis (commonest eye feature) or anterior uveitis (painful red eye)
Urethritis (dysuria, discharge — even if post-enteric)
Signs
Swollen tender joint(s) — typically asymmetric lower limb
Entheseal tenderness (Achilles, plantar fascia)
Keratoderma blennorrhagica: painless papular rash on soles of feet (resembles pustular psoriasis)
Circinate balanitis: painless ulceration on glans penis
Nail changes (onycholysis, nail pitting — overlap with psoriatic arthritis)
Investigations
First-line
Inflammatory markersCRP and ESR typically raised during acute phase
Joint aspirationIf monoarthritis — exclude septic arthritis and crystal arthropathy. Sterile inflammatory fluid
Sexual health screeningChlamydia NAAT (first-void urine or swab) — screen ALL young adults with reactive arthritis
Second-line
Stool cultureIf post-enteric: Campylobacter, Salmonella, Shigella, Yersinia
HLA-B27Positive in ~50–80%. Supports diagnosis but not diagnostic alone
X-ray sacroiliac jointsIf axial symptoms — may show sacroiliitis
Specialist
MRI sacroiliac jointsMore sensitive than X-ray for early sacroiliitis — bone marrow oedema
Management
BSR/BHPR guidelines and expert consensus1
Acute management
- NSAIDs (naproxen, ibuprofen, etoricoxib): first-line for joint inflammation
- Intra-articular corticosteroid injection for persistent monoarthritis
- Rest and physiotherapy
2
Treat underlying infection
- If Chlamydia detected: doxycycline 100 mg BD for 7 days (or azithromycin 1 g stat) + partner notification
- GI infection: usually resolved by time arthritis develops — antibiotics not routinely indicated
3
Persistent/chronic reactive arthritis (>6 months)
- Sulfasalazine: first-line DMARD if persistent joint inflammation
- Methotrexate: alternative DMARD
- Anti-TNF therapy: for severe refractory cases
Complications
- Chronic arthritis: ~20% develop chronic joint inflammation lasting >6 months
- Anterior uveitis: Painful red eye — ophthalmology referral if suspected
- Cardiac: Rarely aortitis or conduction abnormalities
- Recurrence: Particularly with reinfection or persistent Chlamydia
UKMLA Exam Tips
- 1Asymmetric oligoarthritis (lower limbs) + preceding GI or urogenital infection = reactive arthritis
- 2Classic triad: arthritis + urethritis + conjunctivitis (but full triad only in minority)
- 3Keratoderma blennorrhagica (soles) and circinate balanitis (glans) are highly specific features
- 4Dactylitis ("sausage digit") and enthesitis link reactive arthritis to the spondyloarthropathy family
- 5Always screen for Chlamydia in young adults with reactive arthritis — treat if positive
- 6Self-limiting in ~80% within 6–12 months. DMARDs if persistent
- 7"Can't see, can't pee, can't climb a tree" — classic mnemonic for conjunctivitis, urethritis, arthritis
practicetest your knowledge on reactive arthritisApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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