Crystal Arthropathies

Question · easy

A 52-year-old man presents with an acutely swollen, erythematous, exquisitely tender first metatarsophalangeal joint that awoke him from sleep. Arthrocentesis yields inflammatory fluid. Which synovial fluid finding establishes the diagnosis of gout?

Rhomboid crystals that are yellow when parallel to the polarizing axis Rhomboid crystals that are blue when parallel to the polarizing axis Crystal aggregates that stain with alizarin red Needle-shaped crystals that are yellow when parallel to the polarizing axis

Question · easy

A 60-year-old man with gout has had four flares in the past year and palpable tophi on his elbows. You decide to start urate-lowering therapy. Which statement about its use is correct?

Allopurinol is first-line, started at 100 mg/day and titrated to a serum urate target below 6.0 mg/dL Febuxostat is the preferred first-line agent in all patients Allopurinol should be started at 800 mg/day to rapidly dissolve tophi Urate-lowering therapy should be stopped during an acute flare

Question · medium

A 68-year-old woman with a hot, swollen knee undergoes arthrocentesis. Synovial fluid shows negatively birefringent needle-shaped crystals within neutrophils. Her serum urate drawn during the flare is 5.4 mg/dL. Which is the most appropriate interpretation and next step?

The normal serum urate excludes gout; pursue an alternative diagnosis only Repeat the serum urate immediately; if still normal, no further evaluation is needed The crystals confirm gout, but Gram stain and culture should still be obtained because infection can coexist A normal serum urate during a flare confirms that this is pseudogout rather than gout

Question · medium

A 44-year-old man presents with acute calcium pyrophosphate crystal arthritis (pseudogout) confirmed by rhomboid, positively birefringent crystals. He has no prior joint trauma. Given his age, which underlying condition should you specifically evaluate for?

Hemochromatosis and hyperparathyroidism Hyperthyroidism Alpha-1 antitrypsin deficiency Glucose-6-phosphate dehydrogenase deficiency

Question · hard

A patient with severe tophaceous gout refractory to conventional therapy is started on pegloticase infusions every 2 weeks. Several weeks later his serum urate, previously near zero, is now 6.4 mg/dL on two consecutive pre-infusion checks. What is the most likely explanation and appropriate action?

Anti-drug antibody formation rendering pegloticase ineffective; discontinue it Dietary non-adherence; reinforce purine restriction and continue unchanged Concurrent allopurinol is antagonizing pegloticase; stop allopurinol Expected pharmacologic waning; increase the pegloticase dose