Disseminated osteomyelitis or bone metastases of breast cancer: ¹⁸F-FDG-PET/CT helps unravel an unusual presentation

We present a case wherein striking ¹⁸F-FDG-PET/CT findings initially considered consistent with recurrent disseminated skeletal metastases of breast cancer were later identified as an unusual presentation of disseminated chronic pyogenic osteomyelitis with Staphylococcus aureus and warneri identified on microbiological culture. A 76-year-old female with previous history of breast cancer presented with a 6-month history of pyrexia, myalgia and weight loss. Besides neutrophilia and elevated C-reactive protein, other blood indices, cultures and conventional imaging failed to identify the cause of pyrexia of unknown origin (PUO). ¹⁸F-FDG-PET/CT demonstrated multiple widespread foci of intense FDG uptake in lytic lesions throughout the skeleton. Coupled with previous history of malignancy, findings were strongly suggestive of disseminated metastases of breast cancer. Through targeting an FDG avid lesion, ¹⁸F-FDG-PET/CT aided CT-guided biopsy, which instead identified the lesions as chronic pyogenic osteomyelitis. Following prolonged antibiotic therapy, repeat ¹⁸F-FDG-PET/CT demonstrated significant resolution of lesions. This case demonstrated an unusual presentation of disseminated osteomyelitis on ¹⁸F-FDG-PET/CT and highlighted the use of ¹⁸F-FDG-PET/CT as a trouble shooter in PUO but demonstrated that unusual presentations of benign or malignant pathologies cannot always reliably be differentiated on imaging alone without aid of tissue sampling. Furthermore, this case highlights the potential role ¹⁸F-FDG-PET/CT could provide in assessing response to antibiotic therapy.