Infection induced systemic illness characterised primarily by an inflammatory synovitis from which viable microorganisms cannot be cultured

Aetiology

• Most common preceding infections are urogenital (e.g. chlamydia, neisseria) and enterogenic (e.g. salmonella, campylobacter)
• HLA B27 positive
• Early adulthood, commonly presents between the age of 20 and 40
• Equal sex distribution

Pathophysiology

• Occurs in response to an infection in another part of the body
• Large joints e.g. the knee become inflamed around 1‐3 weeks following the infection
• The infection triggers an autoimmune arthropathy

Clinical features

Symptoms

• Arthritis - tends to be a peripheral arthritis beginning 1-4 weeks after infection
  • Commonly an asymmetrical oligoarthritis, but may be polyarticular/monoarticular
  • Most commonly affects the large joints of the lower limbs
• Axial arthritis, particularly of the sacroiliac joints and lumbosacral spine is another presentation
  • This occurs in up to 40% of patients and is associated with HLA-B2
• Constitutional symptoms including fever, fatigue, malaise - can be severe and mimic sepsis (which needs to be excluded)
• Enthesitis manifesting as Achilles tendonitis or plantar fasciitis

Signs

• Dactylitis
• Mucocutaneous lesions
  • Keratodema blenorrhagica
  • Circinate balanitis
  • Painless oral ulcers
  • Hyperkeratotic nails
• Ocular lesions (uni or bilateral) - conjuntivitis, iritis, anterior uveitis