A 28-year-old man comes to the clinic because of a 5-day history of right knee pain and sw… — USMLE Step 2 CK

A 28-year-old man comes to the clinic because of a 5-day history of right knee pain and swelling. He reports that the knee feels stiff and is difficult to bend. He also notes a gritty sensation in both eyes and mild burning upon urination for the past two days. One month ago, he had an episode of severe diarrhea with abdominal cramping that resolved without treatment after a week. His temperature is $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), blood pressure is $122/78\text{ mm Hg}$ , and pulse is $84/\text{min}$ . Physical examination shows a swollen, warm, and tender right knee with a moderate effusion. Conjunctival injection is present bilaterally. Arthrocentesis of the right knee yields synovial fluid with a leukocyte count of $18,000/\text{mm}^3$ and no crystals. Gram stain of the fluid is negative. Which of the following is the most appropriate next step in the management of this patient's joint condition?

Prescribe oral diclofenacAnswer
B
Administer intravenous ceftriaxone and oral azithromycin
C
Prescribe oral ciprofloxacin
D
Order HLA-B27 testing
E
Measure serum uric acid level

Answer

Prescribe oral diclofenac

The correct action is to prescribe an NSAID. The patient's history of preceding diarrhea followed by the triad of arthritis, conjunctivitis, and urethritis strongly indicates reactive arthritis. Because this is a sterile, immune-mediated inflammatory process, the first-line treatment for the symptomatic relief of joint pain and swelling is an NSAID such as diclofenac, naproxen, or ibuprofen.

Step-by-Step Solution

Analyze the clinical presentation and recent medical history.

The patient presents with asymmetric oligoarthritis, conjunctivitis, and urethritis one month after a diarrheal illness.

Identifying the classic triad (arthritis, conjunctivitis, urethritis) and the preceding trigger is essential for diagnosing reactive arthritis.

Evaluate the synovial fluid analysis.

The fluid is inflammatory (leukocyte count

18,000/\text{mm}^3

) but sterile (negative Gram stain and no crystals).

This rules out septic arthritis (which typically has leukocytes >

50,000/\text{mm}^3

and positive cultures) and crystal arthropathies.

Determine the optimal initial treatment for the diagnosed condition.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the correct choice.

NSAIDs are the standard first-line therapy for managing the inflammatory joint symptoms of reactive arthritis.

Key Concept

Reactive arthritis typically presents with a triad of asymmetric oligoarthritis, conjunctivitis, and urethritis following a gastrointestinal or genitourinary infection, and is managed initially with NSAIDs.

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