Use of Subtraction PET to Identify the Source of Recurrent Sepsis After Bomb Blast Injury. Case Report

Timely diagnosis of osteomyelitis is essential for its successful treatment but it is often difficult to recognise despite extensive radiological workup. We outline a case of recurrent sepsis over a 7-year period in a patient injured by a car bomb blast and the use of an innovative imaging technique to localise two culprit foci of osteomyelitis. This was a prolonged and difficult diagnosis due to extensive shrapnel injury and associated inflammation as well as significant anatomical disruption from the blast. Sites of inflammation associated with shrapnel injury acted as decoys to the true foci of active infection on fluorodeoxyglucose (FDG), positron emission tomography/computed tomography (PET/CT) and an additional technique was required to differentiate these. This involved administering a course of antibiotics between two separate FDG-PET/CT scans and is known as subtraction PET. Two sites of osteomyelitis were identified among 20–30 other sites of benign granulomatous inflammation and calcification. These two sites of infection were characterised by a significant drop in tracer uptake on FDG-PET/CT after a course of antibiotics while tracer uptake at the remaining sites remained relatively unchanged. This ultimately guided surgical excision of the sequestra, and at follow-up of 2 years, the patient has experienced no further septic episodes.