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Case 1: Febrile toddler with refusal to walk.

A 22-month-old boy presented to the emergency department with three days of fever up to 39.5°C, one day of apparent right knee pain and refusal to ambulate. There was no history of sick contacts, trauma, cough, congestion, emesis or diarrhea. On physical examination, he had a temperature of 38.5°C, a pulse rate of 102 beats/min, a respiratory rate of 25 breaths/min and a blood pressure of 95/46 mmHg. The extremity examination revealed no obvious joint swelling; however, a decreased passive and active range of motion of the right knee and right hip with guarding was noted. Radiographs of the lower extremity were normal. Laboratory results revealed a white blood cell count of 17.8×109/L, erythrocyte sedimentation rate of 52 mm/h and a C-reactive protein (CRP) level of 7.1 mg/L. Aspiration of the knee joint was dry, and intravenous ceftriaxone was started after blood cultures were drawn. Magnetic resonance imaging of the right leg failed to be completed due to inadequate sedation; a three-phase bone scan was performed instead. Both the Lyme titre and the blood culture returned negative after 48 h. Based on the following results, a comprehensive physical examination was repeated, with significant pain elicited with extension of the hip and with flexion of the hip against resistance. Repeat laboratory testing showed a CRP level of 18.9 mg/L, and a computed tomography (CT) of the abdomen and pelvis was obtained (Figure 1). 
 
 
 
Figure 1 
 
Computed tomography (CT) of the abdomen and pelvis showing multiseptated psoas abscess (arrows)