A 43-year-old woman is evaluated for a 3-day history of left knee pain and swelling. Similar episodes have occurred in either knee as well as the left wrist during the past 2 years. She also reports a sense of generalized weakness, and has experienced constipation and vague abdominal discomfort during the past year. Because of her constipation, her thyroid-stimulating hormone level was recently measured and found to be normal. She takes no medications. 

On physical examination, vital signs are normal. The left knee is warm with a moderate- to large-sized effusion, and decreased range of motion is noted. Proximal muscle strength is normal . 

Radiographs show a thin white line at the chondral surfaces of both knees and at the pubic symphysis. 

Joint aspiration of the left knee shows a leukocyte count of 35,000/µL, with 90% neutrophils; polarizing microscopy shows numerous positively birefringent rhomboid crystals within neutrophils.