18F-FDG PET/CT as a modality for the evaluation of persisting raised infective markers in patients with spinal tuberculosis

Abstract

The aim of the study was to investigate the differences in participant characteristics between positive and negative, positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography (18F-FDG PET/CT) activity at the spinal tuberculosis (TB) site following 12 months of the appropriate chemotherapy therapy for spinal TB. A secondary aim of the study was to determine whether erythrocyte sedimentation rate (ESR) levels could be used as a reliable marker of TB activity and/or treatment success of spinal TB, especially in a high HIV-positive population. Patients and methods: All patients who were treated for spinal TB and underwent an 18F-FDG PET/CT scan were considered for inclusion. PET/CT positive patients underwent a spinal biopsy which was sent for microscopy, Gram staining, Gene Xpert (GXP) polymerase chain reaction (PCR) and histology. Patients in the PET/CT positive group underwent a repeat MRI scan and biopsy at the completion of treatment to investigate the potential presence of resistance or ongoing active spinal TB. Results: A total of 18 patients were included in the study: five patients were allocated to the PET/CT positive group and 13 to the PET/CT negative group. The PET/CT negative group was significantly older (p=0.016) and had significantly fewer TB-infected vertebrae (p=0.010) than the PET/CT positive group. Two patients, one in each group, were found to have drug-resistant spinal TB. At the 12-month follow-up visit, two patients (40%) in the PET/CT positive group and three patients (30%) in the PET/CT negative group were still complaining of back pain. All smear microscopy results of the PET/CT positive patients who underwent a repeat biopsy were negative after the conclusion of treatment; culture results (n=4/4) were also negative. GXP PCR results were positive in four and negative in one case. Only one of four samples showed classic TB signs on histology. Conclusion: This study is the first to report on biopsies done from a PET/CT positive site, after 12 months of anti-tubercular treatment. It is not unlikely that PET/CT is over-sensitive and can show metabolic activity in areas of sterile inflammation, and future studies are necessary to evaluate this.