Gout vs Pseudogout (CPPD)
How to tell Gout and Pseudogout (CPPD) apart when a board question makes them look alike.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
Crystal birefringence on polarized synovial fluid microscopy is the key discriminator.
Side by side
Acute monoarthritis with needle-shaped negatively birefringent monosodium urate crystals indicates gout.
Acute arthritis, often in an older patient and larger joints, with rhomboid positively birefringent crystals indicates CPPD.
Supersaturated uric acid forms monosodium urate crystals that trigger intense neutrophilic synovitis.
Calcium pyrophosphate crystal deposition in cartilage causes acute inflammatory flares and chondrocalcinosis.
Synovial fluid in gout shows needle-shaped negatively birefringent crystals and inflammatory WBC counts often 2000 to 50000 per uL; serum urate can be normal during a flare.
CPPD fluid shows rhomboid weakly positively birefringent crystals, and knee radiographs often show chondrocalcinosis in menisci or articular cartilage.
The trap
A painful red joint with fever can look septic or gouty, and serum urate can mislead; definitive branching requires arthrocentesis with crystal analysis and Gram stain before assuming noninfectious arthritis.
The repair move
Next best step: perform urgent arthrocentesis in any hot swollen monoarthritis, send cell count, Gram stain, culture, and crystal analysis, then treat confirmed CPPD or gout flare with NSAID or colchicine 1.2 mg then 0.6 mg one hour later if renal function allows, while reserving empiric antibiotics for septic concern.
Try a free question
CoreA 62-year-old man has abrupt first metatarsophalangeal pain and swelling overnight. BP 138/84 mm Hg, HR 96/min, temp 37.5 C. Joint aspiration shows needle-shaped negatively birefringent crystals and no organisms. What is the next best step in management?
Show answer and explanation
Answer: B. Treat acute flare with NSAID or colchicine. Crystal-proven acute gout flare is treated with anti-inflammatory therapy such as NSAID or colchicine.
Why the other choices are tempting
- A. Wrong because initiating high-dose urate-lowering therapy during untreated acute flare can worsen symptoms.
- C. Wrong because cultures are negative and there is no evidence of septic arthritis.
- D. Wrong because operative washout is not routine for uncomplicated crystal-proven gout.
- E. Wrong because treatment should not be delayed when diagnostic aspiration already confirms gout.
Flashcards
Tap a card to flip it.
Which polarized microscopy result identifies gout in an acutely inflamed joint?
Needle-shaped negatively birefringent crystals identify gout.
Which crystal morphology is typical of pseudogout in an older patient with knee effusion?
Rhomboid weakly positively birefringent crystals support pseudogout.
Quick answers
What is the fastest way to tell Gout from Pseudogout (CPPD)?
Crystal birefringence on polarized synovial fluid microscopy is the key discriminator.
What is the key clue for Gout?
Acute monoarthritis with needle-shaped negatively birefringent monosodium urate crystals indicates gout.
What is the key clue for Pseudogout (CPPD)?
Acute arthritis, often in an older patient and larger joints, with rhomboid positively birefringent crystals indicates CPPD.
What is the common trap with Gout vs Pseudogout (CPPD)?
A painful red joint with fever can look septic or gouty, and serum urate can mislead; definitive branching requires arthrocentesis with crystal analysis and Gram stain before assuming noninfectious arthritis.