A 42-year-old man presents to your office with acute left knee pain and difficulty walking.

The patient presents with an acutely inflamed joint and fever, raising concern for septic arthritis. A history of gout does not exclude infection. The first and most urgent step in any monoarthritis with systemic signs (fever) is joint aspiration to assess for crystals, white cells, and organisms.

Toronto Notes 2023 – Rheumatology, “Monoarthritis”:

“Always rule out septic arthritis in a hot, swollen joint, especially when fever is present. Joint aspiration is essential to differentiate infection from crystal arthropathy.”

MCCQE1 Objectives (Medicine > Rheumatology > 49-1):

“Candidates must identify red flags for septic arthritis and understand that arthrocentesis is the first step in diagnosis and management.”

Initiating NSAIDs or acetaminophen without diagnosis (C, D) can delay appropriate care. Radiographs (B) do not help differentiate gout from infection acutely. Blood cultures (E) may help, but aspiration is more diagnostic.

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