A 58-year-old man comes to the office due to a hard mass on the posterior left elbow. The mass has been growing for the past 3 years. The patient has had no fever, pain, weight loss, or trauma. Medical history includes hypertension, chronic kidney disease, and gout. On examination, there is a 3 × 3 cm, nontender, hard mass just under the skin in the posterior left elbow. The elbow is not red, warm, or tender. Elbow imaging shows a 3-cm, soft tissue mass and bone erosions with overhanging edges of cortical bone at the olecranon process. Serum creatinine is 1.7 mg/dL. Which of the following conditions most likely explains this patient's findings?

Question

A 58-year-old man comes to the office due to a hard mass on the posterior left elbow.  The mass has been growing for the past 3 years.  The patient has had no fever, pain, weight loss, or trauma.  Medical history includes hypertension, chronic kidney disease, and gout.  On examination, there is a 3 × 3 cm, nontender, hard mass just under the skin in the posterior left elbow.  The elbow is not red, warm, or tender.  Elbow imaging shows a 3-cm, soft tissue mass and bone erosions with overhanging edges of cortical bone at the olecranon process.  Serum creatinine is 1.7 mg/dL.  Which of the following conditions most likely explains this patient's findings?

Quizplus · Accepted Answer

Explanation: This patient has tophaceous gout affecting the olecranon bursa. The olecranon bursa is a fluid-filled synovial sac between the olecranon process and the skin that alleviates friction at the bony prominence. Gout can affect superficial bursae (eg, olecranon, prepatellar) in multiple ways: Acute bursitis in a gout flare, presenting with erythema, warmth, and swelling Chronic bursitis, presenting with a large, rounded, fluctuant effusion Bursal tophus, manifesting as a slowly enlarging, hard mass (as in this patient), sometimes with mild inflammatory changes Acute bursitis is painful due to the rapidly escalating inflammation; in contrast, chronic bursitis and bursal tophus typically have minimal or no pain because the accompanying inflammation is generally indolent. Tophi (ie, large aggregates of monosodium urate crystals) may also form in the nearby humeroulnar joint or other types of soft tissues (eg, ligaments, tendons). Tophi often trigger a chronic inflammatory response in the surrounding tissue and bone, resulting in bone erosions with overhanging edges of cortical bone on imaging. Urate is intrinsically radiolucent but can become radiopaque when calcium precipitates with urate in a tophus. Risk factors for tophus formation include chronically untreated gout and chronic kidney disease (CKD) (due to decreased uric acid excretion); conversely, chronic hyperuricemia can cause or worsen CKD due to nephrolithiasis and urate deposition in the renal interstitium (ie, urate nephropathy). bone erosions (Choice A) Phosphorus retention and reduced production of 1,25-dihydroxyvitamin D in CKD can lead to secondary hyperparathyroidism and abnormal bone turnover. The resulting skeletal manifestations (ie, CKD-mineral and bone disorder) can include bone pain, fragility fractures, and cystic lesions. However, these findings are usually seen in end-stage renal disease, and soft tissue mass lesions are not typical. secondary hyperparathyroidism (Choice B) Chronic olecranon bursitis is characterized by synovial fluid accumulation within the bursa, most often due to repetitive friction. It presents with a round, fluctuant swelling, not a hard mass. round, fluctuant swelling (Choice C) Osteoarthritis is associated with osteophytes, joint space narrowing (due to cartilage degeneration), subchondral sclerosis, and subchondral cysts. A soft tissue mass and bone erosions are not characteristic. Osteoarthritis typically affects the knees, hips, and hands; elbow involvement is rare. Osteoarthritis (Choice D) Osteosarcoma presents as a primary bone malignancy in adolescents or as a result of malignant transformation of underlying bone pathology (eg, Paget disease) in those age >65. On x-ray, periosteal reaction resulting in sunburst or Codman triangle patterns is typically present. x-ray Educational objective: Gout can cause acute bursal (eg, prepatellar, olecranon) inflammation, chronic bursal swelling, or tophus deposition in the bursa. Tophus induces chronic inflammation in the surrounding soft tissue and bones, which can result in erosions and overhanging edges of cortical bone on imaging. References: Common superficial bursitis. (http://www.ncbi.nlm.nih.gov/pubmed/28290630)

A 58-Year-Old Man Comes to the Office Due to a Hard