Head-to-Head Comparison Between ¹⁸F-FDG PET and Leukocyte Scintigraphy to Monitor Treatment Responses in Necrotizing Otitis Externa

Background: Necrotizing otitis externa (NOE) is a rare disease associated with high morbidity and mortality, and there is currently no available accurate biomarker to assess treatment responses. The aim of the current study was to evaluate and directly compare the diagnostic performances of 18-Fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG PET) and labeled leukocyte scintigraphy (LS) to monitor treatment responses in NOE.

Methods: Consecutive patients with NOE who underwent ¹⁸F-FDG PET at the end of antibiotic therapy and planar as well as single photon emission computed tomography-labeled leukocyte scintigraphy after completing the initial antibiotic treatment were retrospectively included. Semiquantitative analyses were performed to determine the ratios of affected/nonaffected sides for PET and 4 hour and 24 hour LS acquisitions as well as the kinetic PET ratios (at diagnosis and post-treatment) and LS (4 and 24 hours). The final treatment responses were assessed by 2 experienced ENT physicians based on clinical, otoscopic, and biological data and subsequent 3-month follow-up.

Results: Seventeen patients (74.0 ± 10.6 years old, 5 women) were included. The best diagnostic performances were obtained with the PET maximum standardized uptake value (SUV_max)-lesion-to-background ratio and the tomographic LS lesion-to-background ratio at the 4-hour acquisition timepoint (thresholds of 4.1 and 1.19, yielding accuracies of 100% and 88%, respectively). In the multivariate analysis, the PET SUV_max-lesion-to-background ratio was the only predictive factor of recovery when associated with all clinical parameters (P < .001).

Conclusion: ¹⁸F-FDG PET is the first-line imaging modality for evaluating NOE treatment responses, with excellent diagnostic performances. LS with only 4-hour acquisitions appeared to suffice to evaluate NOE treatment responses. Both biomarkers constitute early prognostic biomarkers for predicting antibiotic treatment response in patients with NOE.

Trial registration: The institutional ethics committee (Comité d'Ethique du CHRU de Nancy) approved the evaluation of retrospective patient data, and the trial was registered at ClinicalTrials.gov (n°2023PI003-404).