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Difficulty: MediumRheumatology and Immunology

A 26-year-old man comes to the clinic due to a 4-day history of right knee pain and swelling, as well as pain at the back of his left heel. He reports that the knee feels stiff in the morning and improves slightly as he moves around during the day. Four weeks ago, he experienced a brief episode of watery diarrhea, abdominal cramps, and a low-grade fever that resolved spontaneously after 3 days. He has no other medical conditions and takes no medications. He is sexually active with a new female partner and uses condoms inconsistently. His temperature is 37.2∘C37.2^\circ\text{C} (99.0∘F99.0^\circ\text{F}), blood pressure is 118/76 mmHg118/76\text{ mmHg}, and pulse is 82/min82/\text{min}. Physical examination shows a swollen, warm, and tender right knee with a palpable effusion. There is also pronounced tenderness over the insertion of the left Achilles tendon. Arthrocentesis of the right knee yields yellow, slightly cloudy synovial fluid with a leukocyte count of 22,000/mm322,000/\text{mm}^3 (75%75\% neutrophils). Gram stain shows no organisms, and polarized light microscopy reveals no crystals. Which of the following is the most appropriate next step in management?

  1. Oral naproxenAnswer
  2. B
    Intravenous ceftriaxone and vancomycin
  3. C
    Intravenous ceftriaxone and oral azithromycin
  4. D
    Oral ciprofloxacin
  5. E
    Oral allopurinol

Answer

Oral naproxen
The correct answer is oral naproxen. This patient's presentation of an acute, asymmetric monoarthritis (right knee) and enthesitis (Achilles tendon tenderness) following a self-limited diarrheal illness is highly characteristic of reactive arthritis. Reactive arthritis is an autoimmune spondyloarthropathy that typically develops 1 to 4 weeks after a gastrointestinal infection (e.g., Campylobacter, Salmonella, Shigella) or genitourinary infection (e.g., Chlamydia trachomatis). Synovial fluid analysis classically reveals an inflammatory effusion (leukocyte count between 2,0002,000 and 50,000/mm350,000/\text{mm}^3) with a negative Gram stain and culture, confirming that the joint is sterile. The first-line treatment for managing the acute symptoms of reactive arthritis is nonsteroidal anti-inflammatory drugs (NSAIDs) such as naproxen or ibuprofen.

Step-by-Step Solution

1
Analyze the patient's history and timeline.
The patient developed an asymmetric monoarthritis and enthesitis (Achilles tendon tenderness) 4 weeks after an episode of acute gastroenteritis.
Establishing the sequence of an antecedent infection followed by sterile joint inflammation is key to diagnosing reactive arthritis.
2
Interpret the synovial fluid analysis.
The fluid has 22,000/mm322,000/\text{mm}^3 leukocytes (inflammatory but typically less than the >50,000/mm3>50,000/\text{mm}^3 seen in septic arthritis), negative Gram stain, and no crystals.
This rules out crystal arthropathies (gout/pseudogout) and makes a bacterial septic arthritis highly unlikely, confirming an immune-mediated inflammatory process.
3
Determine the appropriate therapy for the diagnosed condition.
The diagnosis is reactive arthritis. The first-line therapy is nonsteroidal anti-inflammatory drugs (NSAIDs) such as naproxen.
Post-enteric reactive arthritis is a sterile autoimmune process; therefore, treating with NSAIDs is the standard of care to manage inflammation and pain.

Key Concept

Diagnosis and management of reactive arthritis
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Topics

Rheumatology and Immunology

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