Diffusion-weighted Magnetic Resonance Imaging as a Novel Imaging Modality in Assessing Treatment Response in Necrotizing Otitis Externa.

Objective: To report our initial experience of diffusion-weighted magnetic resonance imaging (DW-MRI) as a novel imaging tool for assessing and monitoring treatment response in necrotizing otitis externa (NOE).

Patients: Seven adults with a diagnosis of NOE on both clinical and computed tomography (CT) criteria who were subsequently monitored with at least two echoplanar DW-MRI investigations were included in this retrospective longitudinal observational study.

Intervention: Patients underwent magnetic resonance imaging (MRI), including echoplanar diffusion-weighted sequences, within 2 weeks of diagnosis of NOE to determine the extent of infection and to provide a baseline scan for monitoring response to treatment. Repeated imaging was undertaken after the agreed initial course of antimicrobial therapy was completed.

Main Outcome Measure: The primary outcome measure for complete treatment response was complete resolution of high inflammatory signal on the DW-MRI apparent diffusion coefficient (ADC) map. This was correlated to clinical, biochemical, and other MRI measures of disease resolution.

Results: Baseline DW-MRI was carried out in all but one patient within 2 weeks of the initial diagnostic CT scan. Patients had between one and three further DW-MRI scans, at a mean interval of 4.4 months from the initial scan (range, 2-8 months). The decision to terminate or continue therapy correlated with ADC signal findings on DW-MRI in all cases. In comparison, conventional MRI sequences performed less well, as there was some degree of persistent residual soft tissue changes in all cases.