Laboratory and imaging findings of necrotizing otitis externa are associated with pathogen type and disease outcome: A retrospective analysis.

Objective: To examine associations of laboratory and imaging data with diagnostic parameters of necrotizing otitis externa (NOE) and its severity, and to compare between bacterial and fungal infections. Methods: Records of patients diagnosed with NOE during 2010–2018 at the Department of Otolaryngology, Head and Neck Surgery were reviewed retrospectively for demographics; disease characteristics; and laboratory, scintigraphy, and imaging results. Results: Of 48 patients with NOE, the mean age is 73±11.6 years; 32 (67%) were males; 83% had diabetes mellitus. Common pathogens were pseudomonas (49%) and fungi (33%). Sensitivities of the technetium-scan (SPECT ratio ≥1.5), temporal bone computed tomography (CT), and gallium-scan (SPECT ratio ≥1.3) were: 78.7%, 48.8%, and 31.4%, respectively. Gallium-scan results correlated positively with CT bone involvement (p=0.002) and hospital length of stay (p=0.0014). C-reactive protein (CRP) level correlated with hospital length of stay (p=0.028) and positive technetium-scan results (p=0.012). Fungal infection had a higher technetium SPECT ratio (2.16 vs. 1.77, p=0.04), gallium SPECT ratio (1.4 vs. 1.2, p=0.02), longer duration of systemic treatment (87.4 vs. 37.9 days, p=0.014), and longer hospital length of stay (31.6 vs. 15.2 days, p=0.004) compared to non-fungal infection. Eight (17%) patients had responded poorly to treatment. Fungal pathogens, facial nerve paresis, extra-auricular, and bilateral disease were more prevalent among the non-responders. Conclusion: The technetium scan has higher sensitivity than temporal bone CT for diagnosing NOE. The gallium scan and CRP correlated well with hospital length of stay. A high rate of fungal infection was found, with significantly higher technetium and gallium SPECT ratios and worse outcome compared to bacterial infection. Fungal NOE remains therapeutically challenging.