A 26-year-old man comes to the office for evaluation of left knee pain and swelling. The patient first noticed the pain 3 months ago after going on a short run. His knee has progressively become more painful, and he is now unable to run short distances without significant pain. The patient has tried ice and ibuprofen with no relief, and compression wraps have only made the pain worse. He has no chronic medical conditions, and his only surgery is an enucleation for retinoblastoma when he was an infant. Temperature is 37.2 C (99 F), blood pressure is 130/80 mm Hg, and pulse is 84/min. BMI is 22 kg/m². The left knee appears swollen, but there is no overlying rash or skin lesion. The left knee has full range of motion with no crepitus, but deep palpation over the distal thigh is associated with pain. X-ray of the knee shows a lytic lesion that has ill-defined margins on the femoral condyle and is surrounded by concentric layers of reactive bone. Which of the following is the most likely diagnosis in this patient?

Question

Quizplus · Accepted Answer

This patient with a history of retinoblastoma has a lytic bone lesion in the distal femur with "sunburst" periosteal reaction (concentric layers of reactive bone), raising strong suspicion for osteosarcoma. Most cases arise in children or adolescents at long-bone metaphyses (site of greatest bone proliferation) and present with unilateral pain and swelling; x-rays generally show a lytic bone lesion, sunburst periosteal reaction, and/or Codman triangle (raised edge of ossified periosteum). "sunburst" periosteal reaction Risk of osteosarcoma is greatest in those with inherited genetic mutations to the tumor suppressor genes RB1 (linked to hereditary retinoblastoma) and TP53 (linked to the congenital cancer disorder Li Fraumeni syndrome). Therefore, patients often have a previous history of other cancers, such as retinoblastoma (RB1) or leukemias, breast tumors, brain tumors, or adrenocortical tumors (TP53). Osteosarcoma can also arise in older adults (usually age >60) in areas of previous bone damage due to Paget disease (most common), irradiation, or benign bone tumors; these individuals are less likely to have inherited genetic mutations. (Choice A) Brodie abscess is a form of chronic osteomyelitis that typically occurs in the femoral or tibial metaphysis in the second decade of life. X-ray typically shows a radiolucent, elongated lesion with surrounding reactive sclerosis. This patient's history of retinoblastoma and sunburst periosteal reaction make osteosarcoma more likely. (Choice B) Langerhans cell histiocytosis is a rare disorder most often seen in children age <3 years. Single or multiple "punched-out," lytic bone lesions are common. This patient's age, history of retinoblastoma, and sunburst periosteal reaction make osteosarcoma more likely. lytic bone lesions (Choice C) Myositis ossificans usually develop at the site of muscle injury (eg, quadriceps contusion); they are marked by an eggshell-appearing periosteal reaction around the area of the muscle injury. A lytic bone lesion would not be seen. (Choice D) Osteoarthritis usually presents with joint pain or stiffness in a middle-age or older adult. Characteristic x-ray findings include joint space narrowing, subchondral sclerosis, and osteophyte formation. osteophyte formation (Choice F) Unicameral bone cysts are simple bone cysts that generally occur in individuals age <20 years. X-rays usually reveal a full-thickness lytic bone lesion with well-defined (not irregular) borders and surrounding reactive sclerosis. lytic bone lesion Educational objective: Osteosarcoma is a primary bone tumor that is often associated with inherited genetic mutations to the RB1 gene, which causes retinoblastoma, and the TP53 gene, which is linked to Li Fraumeni syndrome.

A 26-Year-Old Man Comes to the Office for Evaluation of Left