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.