What are the criteria for terminating treatment for necrotizing (malignant) otitis externa?

BACKGROUND The diagnosis of necrotizing, or “malignant,” otitis externa (NOE) is typically made by the clinical picture of a severe otitis externa, often in a diabetic or immunocompromised patient, with associated skull base soft tissue infection and osteomyelitis, as visualized on magnetic resonance (MR) or computed tomographic (CT) scanning. While treatment efficacy has improved since the condition was first described decades ago, NOE remains a severe infection with potential for significant morbidity and mortality. Bacterial NOE is ideally treated with at least 6 weeks of culture-directed systemic antibiotics, often with infectious disease consultation. Patients presenting with NOE frequently have been previously treated with oral or topical antibiotics, rendering cultures negative. In these cases, many clinicians empirically treat with antipseudomonal antibiotics. Longer therapy may be required with multidrug resistant strains of bacteria such as Pseudomonas aeruginosa, or with molds such as Aspergillus fumigatus. As NOE can mimic squamous cell carcinoma of the external ear canal on physical exam and CT scan, some clinicians biopsy granulation tissue when diagnosis is uncertain or if granulation tissue is present after 6 weeks of treatment. Once clinical exam and laboratory markers have normalized, the otolaryngologist faces the problem of how to determine if treatment has been adequate and can be discontinued with minimal risk of recurrence. As soft tissue involvement is expected to have resolved, the concern is for persistent osteomyelitis. Two questions are important: what is the appropriate duration of antibiotics and how can the clinician tell when the infection is resolved.