A 52-year-old man presents to the emergency department with sudden onset of severe pain, redness, and swelling in his right great toe. He reports that the pain started last night and has progressively worsened. He denies fevers or any trauma to the affected toe. He has a history of hypertension and obesity and takes lisinopril with hydrochlorothiazide. He drinks four beers per week and does not smoke cigarettes. Vital signs are within normal limits. On physical examination, the right first metatarsophalangeal joint is erythematous, warm, and extremely tender to touch. Laboratory tests reveal a normal complete blood count (CBC) and elevated serum uric acid level. Arthrocentesis of the affected joint is performed.
Which of the following findings is most likely to be observed in the synovial fluid?
C) Needle-shaped monosodium urate crystals with negative birefringence
Gout is a form of inflammatory arthritis characterized by sudden, severe attacks of pain, redness, and swelling in joints, often affecting the great toe. Gout typically presents as monoarticular arthritis, meaning it usually affects one joint at a time. The first metatarsophalangeal joint (big toe) is the most commonly affected site, a condition known as podagra. Risk factors for gout include obesity, hypertension, a diet high in purines (such as red meat, seafood, and beer), alcohol consumption, and certain medications like thiazide diuretics. This patient takes hydrochlorothiazide, which increases the amount of urate that is reabsorbed in the proximal renal tubules, increasing serum uric acid levels.
Gout is caused by the deposition of monosodium urate crystals in the joints due to elevated levels of uric acid in the blood (hyperuricemia). These crystals are needle-shaped and exhibit negative birefringence under polarized light microscopy, which is a key diagnostic feature.
Management of acute gout attacks involves nonsteroidal anti-inflammatory drugs (NSAIDs), colchicine, or corticosteroids to reduce inflammation and pain. Long-term management focuses on lowering serum uric acid levels with medications such as allopurinol or febuxostat to prevent future attacks.
Answer choice A: Calcium pyrophosphate dihydrate crystals with positive birefringence, is incorrect. These crystals are associated with pseudogout, which presents differently from gout. Pseudogout usually affects larger joints like the knee or wrist. Gout attacks start suddenly and usually peak around 8-12 hours while pseudogout attacks can start suddenly or be more indolent over several days.
Answer choice B: Gram-positive cocci, is incorrect. The presence of bacteria would suggest septic arthritis, not gout. This patient does not have fever or leukocytosis to suggest septic arthritis.
Answer choice D: Oval fat bodies, is incorrect. Oval fat bodies are typically seen in the urine in nephrotic syndrome, not in synovial fluid analysis.
Answer choice E: Red blood cells, is incorrect. While red blood cells may be present in traumatic arthrocentesis or after hemarthrosis such as in an anterior cruciate ligament tear in the knee, they are not characteristic of gout.
Key Learning Point
Gout is characterized by monoarticular arthritis, elevated serum uric acid levels, and needle-shaped monosodium urate crystals with negative birefringence in the synovial fluid.