Malignant External Otitis
(Necrotizing Otitis Externa; Skull Base Osteomyelitis)
Soft tissue, cartilage, and bone are all affected by malignant external otitis. The osteomyelitis spreads along the base of the skull and may cause cranial neuropathies (VII usually affected first followed by IX, X, and XI) and may cross the midline.
Malignant external otitis occurs mainly in older patients with diabetes or in immunocompromised patients. It is often initiated by Pseudomonas external otitis; methicillin-resistant Staphylococcus aureus (MRSA) has also been identified as a cause. It is characterized by persistent and severe, deep-seated ear pain (often worse at night), foul-smelling purulent otorrhea, and granulation tissue or exposed bone in the ear canal (usually at the junction of the bony and cartilaginous portions of the canal). Varying degrees of conductive hearing loss may occur. In severe cases, facial nerve paralysis, and even lower cranial nerve (IX, X, or XI) paralysis, may ensue as this erosive, potentially life-threatening infection spreads along the skull base (skull base osteomyelitis) from the stylomastoid foramen to the jugular foramen and beyond.
Diagnosis of malignant external otitis is suggested by a high-resolution CT scan of the temporal bone, which may show increased radiodensity in the mastoid air-cell system, middle ear radiolucency (demineralization) in some areas, and bony erosion. Cultures are done, and, importantly, the ear canal must be biopsied to differentiate this disorder from a malignant tumor (eg, squamous cell carcinoma).
Treatment of malignant external otitis is typically with a 6-week IV course of a culture-directed fluoroquinolone (eg, ciprofloxacin, 400 mg IV every 8 hours) and/or a semisynthetic penicillin (piperacillin–tazobactam or piperacillin)/aminoglycoside combination (for ciprofloxacin resistant Pseudomonas). However, mild cases may be treated with a high-dose oral fluoroquinolone (eg, ciprofloxacin, 750 mg orally every 12 hours) on an outpatient basis with close follow-up. Treatment also includes topical ciprofloxacin/dexamethasone preparations (eg, ear drops, impregnated canal dressings) and serial debridement. Hyperbaric oxygen may be a useful adjunctive treatment, but its definitive role remains to be elucidated. Consultation with an infectious disease specialist for optimal antibiotic therapy and duration and with an endocrinologist for strict diabetic control is recommended. Extensive bone disease may require more prolonged antibiotic therapy. Meticulous control of diabetes is essential. Frequent office debridement is necessary to remove granulation tissue and purulent discharge. Surgery usually is not necessary, but surgical debridement to clear necrotic tissue may be used for more extensive infections.