A 10-year-old boy is brought to the office due to left knee pain and difficulty walking. His parents say that he developed knee pain several months ago, but it was mild and did not affect his mobility. Over the past week, the patient has had increasing pain that prevents him from playing soccer or basketball. He describes the pain as continuous, nonradiating, and sometimes worse at night. The patient has taken ibuprofen but it has not relieved the pain. He does not recall any preceding trauma. He has had occasional fever over the last month; temperature today is 37.2 C (99 F). The patient has an antalgic gait and favors the right side. The left knee is swollen and erythematous. A tender, immobile mass is palpated above the left knee. Laboratory results are as follows:
| Leukocytes | 14,600 mm3 |
| Erythrocyte sedimentation rate | 40 mm/hr |
X-ray of the knee shows a central lytic lesion in the distal femur with cortical layering, a "moth-eaten" appearance, and extension into the soft tissue. Which of the following is the most likely diagnosis in this patient?
Ewing sarcoma | |
Epidemiology |
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Clinical features |
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X-ray findings |
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Ewing sarcoma is the second most common malignant bone tumor of childhood (after osteosarcoma) and typically affects white, adolescent boys. The tumor usually occurs in the pelvis or diaphyses of long bones (eg, femur) and often metastasizes early to the lungs, bone, and bone marrow.
Clinical presentation includes subacute or chronic, localized pain and swelling. Pain is often worse at night and with activity and progresses rapidly. Local erythema and warmth are common, and systemic findings (eg, fever, weight loss, leukocytosis, elevated inflammatory markers) may occur, particularly with metastatic disease.
Imaging of Ewing sarcoma classically reveals a lamellated periosteal reaction in which a central, poorly defined lytic lesion is surrounded by concentric layers of new bone ("onion skinning"). A "moth-eaten" or mottled appearance can also occur with extension into soft tissue. Codman triangle is a nonspecific radiographic finding that represents the displacement/elevation of periosteum by underlying tumor and can also be seen in osteosarcoma. Treatment includes chemotherapy as well as surgical resection ± radiation.
(Choice B) Fibrosarcoma is a rare, malignant spindle cell neoplasm that typically presents with a painful mass in patients age >30. X-ray reveals an osteolytic lesion with well-defined or ragged, "moth-eaten" margins.
(Choice C) Giant cell tumor of bone is a benign tumor typically located in the epiphyses of long bones. It presents in young adults with pain and swelling and is characterized by a lytic area with a "soap bubble" appearance on imaging due to bony trabeculae within the lesion.
(Choice D) Juvenile idiopathic arthritis presents with chronic joint pain and swelling and signs of systemic inflammation. X-ray at presentation may reveal soft-tissue swelling and joint effusion.
(Choice E) Multiple myeloma is a malignant plasma cell dyscrasia that generally presents in older adults and is extremely rare in patients age <40. Extensive, punched-out lytic lesions, severe osteopenia, and pathologic fractures are common x-ray findings.
(Choice F) Osteoid osteoma is a benign bone tumor typically found in adolescent boys. It is most commonly located in the proximal femur and causes pain at night that is responsive to nonsteroidal anti-inflammatories (eg, ibuprofen). A small, round lucency is seen on x-ray.
(Choice G) Unicameral bone cysts occur in children and young adults and are typically located at the proximal femur or humerus. A pathologic fracture is the most common presentation, and x-ray reveals a cystic lesion with well-defined margins.
Educational objective:
Ewing sarcomas are malignant tumors that occur most commonly in the pelvis and long bones of white, adolescent boys. Localized pain and swelling can be accompanied by systemic findings and characteristic "onion skinning" (ie, lamellated periosteal reaction) and "moth-eaten" appearance on x-ray.