Disappearance of FDG uptake on PET scan after antimicrobial therapy could help for the diagnosis of Coxiella burnetii spondylodiscitis.

A 55 year-old man was admitted for worsening of a chronic low back pain associated with L4-L5 anterolisthesis, despite taking non-steroidal anti-inflammatory drugs for several months. He had a medical history of high blood pressure and obesity (body mass index, 37 kg/m2). He lived in the countryside but had no direct contact with animals except his dog. There were no fever, chills, sweats or weight loss. C reactive protein (CRP) was <2.9 mg/L. Radiographs showed L4-L5 anterolisthesis with endplate erosions and bony sclerosis (figure 1A). On MRI (figure 1B), there was a significant enhancement of L4-L5 vertebral endplates and paravertebral soft tissues. Positron emission tomography (PET) CT scan showed an intense uptake of the L4-L5 space (figure 1C). Blood and CT-guided discovertebral cultures remained sterile (including for mycobacteria) and 16s PCR and in-house specific Coxiella burnetii PCR were negative. C. burnetii serology (Focus diagnostics Q fever immunofluorescent antibody IgG and IgM test kits) was positive and in favour of a chronic Q fever (phase I, IgG 2048; phase II, IgG 4096; IgM were negative). Brucella and Bartonella were negative. An echocardiogram was performed to exclude vegetations caused by bacterial endocarditis. The patient was treated with doxycycline (200 mg/day) and hydroxychloroquine (400 mg/day) for 10 months. A significant improvement with reduction of the back pain was noticed and the CRP remained <2.9 mg/L. The antibody titres decreased and the pathological uptake of the L4-L5 space on PET scan disappeared when antibiotics were stopped (figure 1D).