19th January 2024

Differential diagnoses

Ankylosing spondylitis – can present similarly to reactive arthritis; however, spinal involvement tends to be symmetrical, and x-rays can reveal the presence of syndesmophytes. AS also tends to also affect peripheral joints less frequently than reactive arthritis.
Psoriatic arthritis – tends to affect mostly distal interphalangeal joints, which can be identified on x-rays
Rheumatoid arthritis – usually presents as a symmetrical polyarthritis and does not affect lumbar spine or sacral joints. Rheumatoid factors and anti-CCP are frequently positive.
Rheumatic fever – associated with an upper respiratory tract infection. Rheumatic fever tends to present as a migratory arthritis in the upper and lower limbs and does not involve the spine. Antistreptolysin-O titre may be positive.
Adult-onset Still’s disease – may also present with fever and joint pain. Joint pain tends to occur in two spikes throughout the day and is associated with a salmon-coloured rash. Serum LDH and ferritin may be elevated.
Enteric arthritis – patients will have a history of inflammatory bowel disease and tend to present with bilateral and symmetrical sacroiliitis. X-rays reveal marginal syndesmophytes in contrast to reactive arthritis, where non-marginal syndesmophytes are usually seen.
Gout – patients usually present with an acutely swollen and tender joint, and distal interphalangeal joint involvement is common. Gout can be differentiated from reactive arthritis by synovial fluid examination, which would reveal crystals in gout.
Septic arthritis – usually affects a single joint, and presents as a swollen, erythematous and warm joint in the presence of a fever. Synovial fluid analysis and culture would reveal a very high white cell count (>50,000mm ³) and neutrophil count >75%, with identification of the underlying organism. Blood cultures may also be positive in septic arthritis.
Post-viral arthritis – parvovirus infection can present with a flu-like illness followed by arthralgia. This tends to mostly demonstrate a symmetrical small joint polyarticular pattern, and patients may often have a maculopapular rash. Serology would reveal the presence of parvovirus B19

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