Coding Accuracy and Contemporary Management of “Malignant” Otitis Externa in a National EHR Network: Evidence for Misclassification

Abstract Malignant otitis externa (MOE), also called skull base osteomyelitis, is an invasive and potentially life-threatening infection. Reports suggest a rising incidence, though it is unclear whether this represents a true increase in disease burden or misclassification within electronic health records (EHRs). This study uses a large national database to characterize epidemiology, management patterns, and outcomes of patients diagnosed with MOE. Retrospective cohort study. A retrospective cohort study of the Epic Cosmos database (2010–2023), a national HIPAA-defined limited EHR dataset, identified all encounters with an MOE ICD-10 code. Data included demographics, comorbidities, antimicrobial prescribing, surgical interventions, complications, and all-cause mortality. A total of 18,323 MOE encounters encompassing 7,866 patients were identified (0.48 per 100,000 encounters; 3.78 per 100,000 patients). The mean age was 59.53 years, with 6.5% pediatric cases. Most patients (90.8%) were managed in the outpatient setting. Diabetes was present in 47.3%, malignancy in 26.0%, and chemotherapy in 7.1%. All-cause mortality was 14.5%. Fluoroquinolones were prescribed in only 39.1% of cases. Less than 75% of antibiotics provided antipseudomonal coverage. Antifungal therapy was rare (3.8% of encounters). Surgical intervention was infrequent (2% of encounters) and most commonly included external auditory canal biopsy or mastoidectomy. Our findings diverge from the classic MOE profile of immunocompromised or elderly diabetics with severe complications requiring inpatient care. We observed predominantly outpatient management, atypical risk factor distributions, and antibiotic use inconsistent with MOE. These results suggest widespread misdiagnosis or miscoding of MOE, highlighting the need for standardized diagnostic criteria and careful interpretation of large EHR datasets.