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Secondary osteonecrosis mimicking a femur bone tumor in an adolescent with juvenile idiopathic arthritis

To the Editor: Osteonecrosis (ON) of the femoral head has been described in patients with sickle cell disease [1], malignancies [2] and juvenile idiopathic arthritis (JIA) receiving prednisone (PDN) [3]. We present a 15-year-oldale with a systemic JIA onset, who developed secondary ON mimicking ‘‘skip’’ lesions of bone malignancy due to its unusual location in the lower part of her right thigh. Fourteen months following diagnosis, while in disease remission, she complained of a persistent femur pain. It was a continuous dull pain, with no history of trauma, aggravated by the routine physical activities, resolving with rest and responding to analgesics. Her previous regimen included methotrexate (MTX) 15 mg/m/week, cysclosporine (CSA) 3 mg/kg/day and PDN 2 mg/ kg for the first 2 months, following tapering that ended to 0.25 mg/ kg/day for the last 5 months. X-rays and MRI revealed lesions in the right femoral diaphysis and distal metaphysis suspicious of an osteosarcoma (Fig. 1). The double phase scan TI-201 did not show any radiotracer uptake and was felt to exclude malignancy. To make a definitive diagnosis, an open biopsy was performed. The specimen consisted of pieces of lamellar bone, woven bone, striated muscle and necrotic material. It was compatible either with a healing bone fracture and/or ON. She was conservatively managed by gradual withdrawal of PDN, restriction of weight bearing; she returned to her regular activities 2 months later. After a 5-year follow-up, her radiographs and MRI showed healing sclerotic lesions of the ON area with no bone marrow oedema or periosteal reaction or any soft tissue mass. ON of the femoral bone in patients with pediatric rheumatic diseases receiving long-term PDN is unusual [4,5]. We assume that PDN was the exclusive contributor to the development of ON, as data on the association of MTX or CSA with ON have not been reported. The femoral head is the most common and clinically significant site of ON, while the femoral shaft of JIA patients has not previously been reported. In adults using steroids or following radiation, insufficient fractures of the sacrum have been misdiagnosed as malignancies [6]. On the other hand, Fujimoto et al. [7] emphasized that a metastatic femur tumor can mimic spontaneous ON and have a misleading appearance on MRI imaging. We were faced with the same dilemma due to the unusual location of the ON lesions and the misleading imaging that was consistent with that of a bone tumor. Thallium scintigraphy was an important piece of data as it appeared inconsistent with malignancy [8]. However, a biopsy might be necessary to support such a diagnosis of ON, as occurred in our patient. This case highlights the importance of including ON in the differential diagnosis for bone pain of any patient receiving steroids.