A 62-year-old female presents with acute pain, redness, and swelling of the first metatarsophalangeal (MTP) joint. Arthrocentesis demonstrates cloudy synovial fluid with negatively birefringent needle-shaped crystals under polarized light microscopy. What is the diagnosis?

Answer and explanation

Correct answer: B. Acute gouty arthritis (podagra)

  1. Step 1: Needle-shaped intracellular crystals with strong negative birefringence (yellow when parallel to the slow axis) are characteristic of monosodium urate.
  2. Step 2: This confirms acute gouty arthritis affecting the first MTP joint (podagra).
Answer
Acute gouty arthritis (podagra).
Why not the others: 'Pseudogout (calcium pyrophosphate dihydrate deposition)' demonstrates positively birefringent, rhomboid-shaped crystals; 'Septic bacterial arthritis' demonstrates bacteria on Gram stain with purulent fluid; 'Osteoarthritis flare' lacks intracellular crystals under polarized microscopy.

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