Gout vs Pseudogout (CPPD)
How to tell Gout and Pseudogout (CPPD) apart when a board question makes them look alike.
Gout is needle-shaped negative birefringence and podagra; pseudogout is rhomboid positive birefringence with chondrocalcinosis, often knee or wrist.
Side by side
Gout causes acute inflammatory arthritis from monosodium urate crystals, classically podagra, tophi, hyperuricemia, and needle-shaped negatively birefringent crystals.
Pseudogout causes calcium pyrophosphate arthritis, often knee or wrist, chondrocalcinosis, and rhomboid weakly positively birefringent crystals.
Urate supersaturation triggers neutrophilic inflammation in joints and soft tissues.
Calcium pyrophosphate deposition in cartilage triggers acute arthritis and radiographic chondrocalcinosis.
Needle-shaped negatively birefringent crystals and first MTP attacks support gout.
Rhomboid positively birefringent crystals, chondrocalcinosis, and knee involvement support CPPD.
The trap
Both cause acute monoarthritis, so crystal shape, birefringence, joint, and x-ray calcification separate them.
Watch it explained
Test it nowThe repair move
For crystal arthritis, read crystal shape and birefringence before relying on joint pain alone.
Try a free question
CoreA 54-year-old man with chronic kidney disease (eGFR 38) wakes with 12 hours of severe pain and swelling at the right first metatarsophalangeal joint. The joint is warm, red, and exquisitely tender. Arthrocentesis fluid shows needle-shaped intracellular crystals that are negatively birefringent under polarized light. Serum uric acid is 9.8 mg/dL. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Acute gout. Acute gout is monosodium urate crystal arthritis with classic podagra (first MTP), needle-shaped negatively birefringent crystals, and hyperuricemia; treatment options are NSAIDs, colchicine, or corticosteroids.
Why the other choices are tempting
- B. Pseudogout has rhomboid POSITIVELY birefringent calcium pyrophosphate crystals, typically in the knee or wrist.
- C. Septic arthritis has positive Gram stain or culture and synovial WBC often >50,000.
- D. Cellulitis is a soft tissue infection without intra-articular crystals.
- E. Reactive arthritis follows GI or GU infection with the triad of arthritis, urethritis, and conjunctivitis.
Flashcards
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What crystal supports gout?
Needle-shaped negatively birefringent monosodium urate crystals support gout.
What imaging clue supports pseudogout?
Chondrocalcinosis supports calcium pyrophosphate deposition disease.
Quick answers
What is the fastest way to tell Gout from Pseudogout (CPPD)?
Gout is needle-shaped negative birefringence and podagra; pseudogout is rhomboid positive birefringence with chondrocalcinosis, often knee or wrist.
What is the key clue for Gout?
Gout causes acute inflammatory arthritis from monosodium urate crystals, classically podagra, tophi, hyperuricemia, and needle-shaped negatively birefringent crystals.
What is the key clue for Pseudogout (CPPD)?
Pseudogout causes calcium pyrophosphate arthritis, often knee or wrist, chondrocalcinosis, and rhomboid weakly positively birefringent crystals.
What is the common trap with Gout vs Pseudogout (CPPD)?
Both cause acute monoarthritis, so crystal shape, birefringence, joint, and x-ray calcification separate them.