Review Question - QID 217006

A 37-year-old woman presents to the emergency department with pain and swelling in her right knee. The pain is severe and non-radiating. It began last night and persisted throughout the day. Over the past 2 months, the patient has also had fatigue, urinary frequency, and constipation. Her medical history includes hypertension and nephrolithiasis which was managed conservatively. The patient takes amlodipine. She drinks 2 alcoholic beverages per week and is recently unemployed. Her temperature is 99.9°F (37.7°C), blood pressure is 140/72 mmHg, pulse is 98/min, and respirations are 18/min. Physical exam reveals a warm, swollen right knee with a positive ballottement test. The patient can range her knee between 0 and 40 degrees without pain. The pain is not reproduced with axial loading of the knee. Serum laboratory results are as follows:

Na+: 138 mEq/L
Cl-: 98 mEq/L
K+: 4.5 mEq/L
HCO3-: 24 mEq/L
BUN: 16 mg/dL
Glucose: 105 mg/dL
Creatinine: 0.8 mg/dL
Uric acid: 5.0 mg/dL
Erythrocyte sedimentation rate (ESR) is 56 mm/h

Which of the following is the most likely cause of this patient’s symptoms?