The flea's knees: A unique presentation of cat scratch disease.

A 4-year-old girl presented to the emergency department with right leg pain and associated limp for one day. There was no trauma or injury; she had no fever or recent illness. Her exam was notable for tenderness and swelling to the right knee, most prominent in the popliteal region. Initial laboratory testing was unremarkable except for a mildly elevated C-reactive protein. She had normal radiographs of the right lower extremity. A soft tissue ultrasound demonstrated popliteal lymphadenopathy, a rare finding in children. Reassessment of the patient revealed cat flea bites to the leg, which prompted concern for Bartonella henselae infection causing Cat-scratch Disease (CSD). The patient was treated empirically with Azithromycin and her Bartonella titers returned two days later consistent with active infection. This is a rare clinical report describing popliteal lymphadenitis and lower extremity arthropathy caused by Bartonella henselae infection secondary to cat flea bites.