A 5-month-old previously healthy, full-term female presented to a pediatric emergency department (ED) with 2 weeks of left leg swelling. Her parents denied any history of trauma, pain, fevers, weight loss, and easy bruising or bleeding, and family history was negative for cancer. The patient had been feeding and eliminating well. The parents said that x-rays of the patient’s left leg were obtained at a different ED soon after they had noted the sudden-onset swelling. At the time they were told that the x-rays were abnormal, and they decided to report to the pediatric ED because authorization for an outpatient magnetic resonance imaging (MRI) study ordered by the patient’s primary pediatrician was taking too long.
In the pediatric ED, the patient was well appearing. Her temperature was 98.42°F; heart rate was 164 beats per minute; respiratory rate was 28 breaths per minute; blood pressure was 127/68 mm Hg (although she was moving while the measurement was obtained); and her oxygen saturation level was 99% on room air. She weighed 6.8 kg.
Physical examination showed significant swelling below the patient’s left knee without erythema, warmth, or apparent tenderness. The infant had intact pulses, no lymphadenopathy, no hepatosplenomegaly, no rash, and no swelling noted elsewhere. She moved all extremities equally with normal range of motion and strength.
Laboratory studies and imaging
Laboratory studies revealed an elevated white blood cell count (20.15 K/uL) as well as an elevated platelet count (722 K/uL) and elevated inflammatory markers (C-reactive protein, 5.0 mg/dL; erythrocyte sedimentation rate, 44 mm/h). A comprehensive chemistry panel, lactate dehydrogenase, and uric acid were unremarkable. Additionally, x-rays of the patient’s left lower extremity and chest were obtained, which preliminarily showed marked periosteal reaction involving the left tibia and fibula and multiple ribs on the left (Figures 1A and 1B).
The differential diagnosis in the ED included trauma, osteomyelitis, and malignancy (Table). Other conditions on the differential for unilateral lower extremity soft tissue swelling can be ruled out by the patient’s age of presentation, other associated symptoms, and pattern of bone involvement.1
Primary bone malignancies such as osteosarcoma and Ewing sarcoma are very rare in infants. Benign bone and soft tissue tumors such as chondroblastomas and osteoid osteomas do not typically present with marked periosteal reaction in multiple areas. Vitamin deficiencies such as scurvy and rickets are not self-limiting and typically present with other clinical findings (eg, petechiae, corkscrew hairs, and gum disease in scurvy). Exposure to medications such as prostaglandin E (eg, in infants with cyanotic congenital heart disease) and vitamin A can be obtained on history.2,3 Prostaglandin E is thought to promote osteogenesis by decreasing bone resorption and vitamin A is thought to regulate osteoblasts and osteoclasts. Accidental and nonaccidental trauma should be ruled out with careful history taking and scrutiny of the distribution of bone involvement.4 Other important diagnoses to include in the differential are infection (eg, osteomyelitis), endocrine disorders, and rare metabolic disorders.