FDG PET/CT is useful for the interim evaluation of response to therapy in patients affected by haematogenous spondylodiscitis

Purpose Antibiotic therapy in patients affected by discitis is often empirical. Therefore, early evaluation of response to therapy is important. In many patients inflammatory indexes are low during all the phases of the diseases or are altered by concomitant diseases. The aim of the study was to assess the possible role of FDG PET/CT for the early evaluation of response to therapy in patients affected by infective discitis, in comparison to C-reactive protein (CRP) serum levels. Methods Enrolled in the study were 38 patients diagnosed with haematogenous infective discitis. Of the 38 patients, 7 had tubercular infection, 1 fungal infection and 30 pyogenic discitis. Four patients were excluded because the second PET/CT scan was not performed. Thus 34 patients (18 women, mean age 64 years) were analysed. All the patients included underwent a FDG PET/CT scan and determination of CRP level at baseline and again 2 to 4 weeks after the start of therapy. The PET results in terms of SUV of the first and second scans (SUV1 and SUV2) and delta-SUVmax were compared to the inflammatory indexes and clinical status during therapy. Results The mean SUVmax at diagnosis was 8.6±3.7. The mean CRP level at diagnosis was 3.8±3.8 mg/dl. A progressive clinical response was seen in 26 patients and 8 patients showed no response. SUV1 was not correlated with the baseline CRP level (CRP1, p00.7) and SUV2 was not correlated with the CRP level at the time of the second scan (CRP2, p0 0.4). In responders, SUV2 and CRP2 were significantly lower than SUV1 and CRP1 (p