Malignant External Otitis
(Skull Base Osteomyelitis; Necrotizing Otitis Externa)
Malignant external otitis, also referred to as skull base osteomyelitis or necrotizing otitis externa, is typically a Pseudomonas osteomyelitis of the temporal bone. Methicillin-resistant Staphylococcus aureus (MRSA) has also been reported as a cause.
Soft tissue, cartilage, and bone are all affected. 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 elderly 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 is based on a high-resolution CT scan of the temporal bone, which may show increased radiodensity in the mastoid air-cell system and middle ear radiolucency (demineralization) in some areas. Identifying bony erosion confirms the diagnosis. Cultures are done, and, importantly, the ear canal must be biopsied to differentiate this disorder from a malignant tumor.
Treatment is typically with a 6-wk IV course of a culture-directed fluoroquinolone (eg, ciprofloxacin, 400 mg IV q 8 hr) 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 po q 12 hr) on an outpatient basis with close follow-up. Treatment also includes topical ciprofloxacin/dexamethasone preparations (eg, ear drops, impregnated canal dressings). 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 may be used for more extensive infections.
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