Necrotizing otitis externa (NOE) is a rare but severe infection of the external ear canal that can progress to osteomyelitis of the temporal bone, often caused by Pseudomonas aeruginosa. Effective management requires prolonged systemic antibiotic therapy, as premature termination increases the risk of relapse. There is ongoing debate regarding the optimal duration of antibiotic treatment and the criteria for discontinuation. Functional imaging techniques, such as 67GaGallium citrate SPECT/CT and 18FFDG-PET/CT, have shown promise in assessing disease activity, but their roles in therapy evaluation remain underexplored. In this study, we describe the radiological disease activity during treatment and we relate activity at cessation of treatment to disease control in patients scanned with 67 GaGa-citrate SPECT/CT and/or 18FFDG-PET/CT. Secondly, inter-rater variability is assessed. Twenty patients with NOE, with a median duration of intravenous treatment of six months (range 1–24 months) were included. Relapse occurred in 3 patients. Qualitative assessment of 95 scans showed slight inter-rater agreement for 67GaGa-citrate SPECT/CT (kappa = 0.167) and fair agreement for 18FFDG-PET/CT (kappa = 0.400). Relapse was seen in patients both with and without complete resolution on imaging. In the semi-quantitative assessment, 67GaGa-citrate SPECT/CT showed a decrease in countsmax ratio (1.93 to 1.35), but an increase in countsmean ratio (1.56 to 1.73) between baseline and end of treatment. 18FFDG-PET/CT showed a 50% reduction in both maximal standardized uptake value, corrected for lean body mass (SULmax) and peak standardized uptake value, corrected for lean body mass (SULpeak) ratios and also a decrease in metabolic tumor volume (MTV) in most cases. Semi-quantitative measurements on 67GaGa-citrate SPECT/CTs and 18FFDG-PET/CTs demonstrated notable variation in NOE. However, our findings suggest that MTV might be a useful parameter in quantifying the 18FFDG-PET/CT result during the course of disease. Although 18FFDG-PET/CT with visual evaluation, potentially alongside MTV, appears to be the most effective, the inter-observer variability emphasizes the necessity for standardized protocols to improve consistency and reliability in clinical practice and to guide clinical decision-making.
Vosbeek et al. (Sat,) studied this question.