A 65-year-old man comes to the office for evaluation of new-onset pain in the right knee. The patient first noticed the pain 3 weeks ago after a long hike in the mountains. The pain has not improved with acetaminophen, and he is now unable to sleep because of it. He has also had intermittent low-grade fevers. The patient has Paget disease of bone, which was diagnosed 10 years ago, and type 2 diabetes mellitus. He drinks alcohol socially but does not use tobacco or illicit drugs. Temperature is 37.2 C (99 F), blood pressure is 120/70 mm Hg, and pulse is 80/min. BMI is 23 kg/m². The right knee has diffuse soft tissue swelling and a small effusion with no surrounding erythema. The distal aspect of the thigh is tender to palpation. X-ray of the right knee reveals medullary and cortical bone destruction with lucent areas and a surrounding periosteal elevation along the distal femur. Which of the following is the most likely cause of this patient's knee pain?

Question

Quizplus · Accepted Answer

Explanation: This patient with Paget disease of bone now has a destructive femoral lesion, raising strong suspicion for osteosarcoma. Most cases occur in a bimodal distribution, as follows: In children and adolescents, osteosarcoma usually develops at the metaphysis of long bones, where cellular turnover is high (primary osteosarcoma). In adults age >40, osteosarcoma usually develops at sites of damaged bone, particularly due to Paget disease of bone, irradiation, or prior benign bone tumor (secondary osteosarcoma). Paget disease of bone is associated with increased bone remodeling and bone overgrowth. Although most cases are asymptomatic, the risk of osteogenic sarcomatous transformation (at sites of bone overgrowth) is several-thousand times greater than the general population. Manifestations of malignant transformation generally include worsened localized pain and soft tissue swelling. Imaging usually shows a destructive bone lesion with a mixture of radiodense and radiolucent areas, a sunburst periosteal pattern, and/or Codman triangle (periosteal elevation). Adults who develop osteosarcoma have a poor prognosis. Imaging (Choice A) Lyme arthritis is a manifestation of Borrelia burgdorferi infection usually characterized by monoarticular arthritis of the knee. However, it typically develops months to years after tick exposure. In addition, although erosion of the joint cartilage or bone can sometimes occur, cortical bone destruction with periosteal elevation would be atypical. (Choice B) Osteoarthritis, characterized by inflammatory destruction of articular cartilage, often involves several joints (eg, knees, hips). Imaging generally shows thickening of subchondral bone, joint space narrowing, and formation of osteophytes. osteophytes (Choice C) Stress fracture is an overuse injury to bone caused by repetitive stress (eg, running on pavement). Although stress fracture can be associated with periosteal elevation, cortical thickening, and sclerosis, the presence of bone destruction with radiolucent areas suggests a neoplastic process. In addition, stress fracture is rare in the femur; most cases occur in the tibia and fibula. cortical thickening (Choice E) Calcium pyrophosphate deposition disease is common in older patients. Symptomatic disease often presents with acute arthritis in the knee (>50% of cases). However, imaging shows cartilage calcification (eg, menisci) and degenerative changes in the joint that are similar to osteoarthritis (eg, subchondral cysts, osteophytes, bone/cartilage fragmentation). cartilage calcification Educational objective: Paget disease of bone is associated with increased bone remodeling, which dramatically increases the risk of osteosarcoma. Most cases present with pain, soft tissue swelling, and hallmark radiographic findings (eg, destructive bone lesion, sunburst periosteal reaction, Codman triangle).

A 65-Year-Old Man Comes to the Office for Evaluation of New-Onset