Disseminated osteomyelitis or bone metastases: FDG-PET/CT helps targeting lesion for biopsy

Learning Objectives 1. Emphasise that FDG-PET/CT alone cannot reliably differentiate between inflammation/infection and malignancy. 2. Emphasise the role of FDG-PET/CT as a problem solving tool in patients with PUO. 3. Highlight the potential role of FDG-PET/CT as a useful tool in monitoring the response to antibiotic therapy.

A 76 year-old woman with history of breast cancer 16 years previously was admitted with a 6 month history of intermittent fevers, night sweats, 18kg weight loss and myalgia. Examination was unremarkable. Admission bloods showed 10,800 neutrophils/mm³ and CRP 155mg/l though septic screen including urine/blood culture was unremarkable. The patient underwent whole-body fluorodeoxyglucose-positron emission tomography (FDG-PET)/CT to determine the cause of pyrexia of unknown origin (PUO). FDG-PET/CT demonstrated multiple widespread foci of intense FDG uptake in lytic lesions throughout the axial/appendicular skeleton (fig1). Though initially thought to be related to widespread bony metastases, CT-guided biopsy of a lytic sacral lesion showed chronic pyogenic osteomyelitis: microbiological culture confirmed Staphylococcus aureus and warneri. A course of levofloxacin and rifampicin led to complete symptom resolution and repeat FDG-PET/CT showed partial resolution of the bone findings. FDG-PET/CT is a useful diagnostic tool in patients with PUO¹. However, it cannot reliably differentiate between inflammation/infection and malignancy; even dual-time-point imaging and SUV values are of little discriminatory value². Understanding of disease behaviour, identification of situations when tissue sampling is needed and close working relationships with clinicians is essential in this setting. In our case FDG-PET/CT was helpful in identifying a biopsy site leading to the diagnosis of infection and the patient recovered fully after antibiotic therapy. As demonstrated in this case, FDG PET/CT may also be useful in monitoring the response to antibiotic therapy³.