Preliminary evidence supporting use of UK consensus definitions for necrotising otitis externa

• UKCCD for NOE has excellent concordance with expert clinical diagnoses. • UKCCD may be used as a risk stratification tool for severe EAC infections. • MRI may distinguish severe EAC infections that cannot be differentiated on CT. Infections of the external ear canal (EAC) exist as a spectrum of disease from severe otitis externa (SOE) to necrotising otitis externa (NOE), but distinguishing between these is challenging. The UK consensus case definition (UKCCD) was established in 2022, but had not yet been assessed in clinical practice. All consecutive adult patients undergoing CT to investigate a diagnosis of possible NOE between November 2018 and October 2019 were prospectively included in the cohort. Clinical diagnosis at baseline and the end of 12 months follow-up were compared to the diagnosis defined by UKCCD. 55 patients were included in the analysis. 27 % (15/55) had an initial clinical diagnosis of NOE, of which 47 % (7/15) did not have changes on CT consistent with NOE. Only 9 % (5/55) patients had an MRI scan performed within 7 days of the baseline CT. At the end of 12 months, 9 % (5/55) patients had a change in diagnosis to or from NOE. All cases diagnosed as NOE by UKCCD had a clinical diagnosis of ‘NOE’ at baseline, while no cases clinically diagnosed as NOE were mislabelled by UKCCD as ‘not NOE’. All cases that had a change of diagnosis in the 12-month period or had an initial CT with no changes consistent with NOE, were captured by the UKCCD category of ‘possible NOE’. Median duration of antibiotics of clinically defined NOE cases were 14 days of intravenous (IQR: 7.3–23.8), 28 days of oral (IQR: 21.0–40.3), and 49.5 days combined (IQR: 29.8–67.3). UKCCD has excellent clinical concordance with clinical diagnosis. Further work is warranted to assess its utility for risk stratification of patients presenting with severe infections of the EAC in a larger cohort.