Rheumatology · Spondyloarthropathies
The facts most likely to be tested
Reactive arthritis is a seronegative spondyloarthropathy that typically presents as an asymmetric oligoarthritis of the lower extremities following a GI or GU infection.
The classic clinical triad consists of urethritis, conjunctivitis, and arthritis, often summarized by the mnemonic 'can't see, can't pee, can't climb a tree'.
Patients frequently test positive for the HLA-B27 allele, which is strongly associated with the development of spondyloarthropathies.
Chlamydia trachomatis is the most common genitourinary trigger, while Campylobacter, Salmonella, Shigella, and Yersinia are the most common gastrointestinal triggers.
Mucocutaneous findings include circinate balanitis (painless penile ulcerations) and keratoderma blennorrhagicum (hyperkeratotic skin lesions on the palms and soles).
Synovial fluid analysis is aseptic (culture-negative) and is used primarily to rule out septic arthritis or crystal-induced arthropathy.
First-line treatment for the arthritis is NSAIDs, while the underlying infection should be treated with appropriate antibiotics if still present.
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A 26-year-old male presents with a 2-week history of painful, swollen right knee and left ankle. He reports a history of dysuria and urethral discharge that resolved 3 weeks ago after unprotected sexual intercourse. Physical examination reveals conjunctival injection and several painless, shallow ulcerations on the glans penis. He has no history of trauma or prior joint disease.
What is the most likely diagnosis?
Reactive arthritis
The patient presents with the classic triad of urethritis, conjunctivitis, and asymmetric oligoarthritis following a Chlamydia infection, which is the hallmark of reactive arthritis.
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Etiology / Epidemiology
Post-infectious autoimmune response, typically Chlamydia trachomatis or GI pathogens (e.g., Campylobacter). Strongly associated with HLA-B27 positivity.
Clinical Manifestations
Classic triad of urethritis, conjunctivitis, and oligoarthritis. Look for dactylitis and circinate balanitis.
Diagnosis
Clinical diagnosis; HLA-B27 testing is supportive but not diagnostic. Synovial fluid analysis rules out septic arthritis.
Treatment
NSAIDs are first-line for joint symptoms. Do not use systemic steroids for long-term management.
Prognosis
Most resolve within 6 months. Chronic disease occurs in 15-20% of patients.
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Epidemiology & Etiology
Occurs 1-4 weeks following a genitourinary or gastrointestinal infection. Chlamydia trachomatis is the most common trigger in young adults. GI triggers include Salmonella, Shigella, and Yersinia.
Pertinent Anatomy
Affects the axial skeleton and large weight-bearing joints of the lower extremities. Enthesitis often involves the Achilles tendon insertion point.
Pathophysiology
Molecular mimicry occurs where bacterial antigens trigger an immune response in genetically susceptible HLA-B27 individuals. Immune complexes deposit in synovial tissues, leading to sterile inflammatory arthritis.
Clinical Manifestations
Patients present with the classic can't see, can't pee, can't climb a tree triad. Look for keratoderma blennorrhagicum (hyperkeratotic skin lesions on palms/soles) and circinate balanitis. Septic arthritis must be excluded in any monoarticular presentation.
Diagnosis
Diagnosis is clinical based on history of antecedent infection and asymmetric oligoarthritis. Synovial fluid analysis is the gold standard to exclude septic arthritis, typically showing inflammatory changes but negative cultures. HLA-B27 is present in 50-80% of cases.
Treatment
NSAIDs (e.g., indomethacin) are the first-line treatment for arthritis. Treat the underlying infection with appropriate antibiotics, though this does not always alter the course of arthritis. Systemic corticosteroids are generally avoided due to lack of efficacy and side effect profile.
Prognosis
Self-limiting in the majority of cases with full recovery within 6 months. Recurrences are common, and 15-20% of patients develop chronic spondyloarthropathy.
Differential Diagnosis
Septic arthritis: usually monoarticular with positive synovial culture
Gonococcal arthritis: migratory polyarthralgia and tenosynovitis
Ankylosing spondylitis: chronic back pain with morning stiffness
Psoriatic arthritis: presence of nail pitting and psoriatic plaques
Rheumatoid arthritis: symmetric small joint involvement with positive RF/anti-CCP