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Malignant External Otitis

(Necrotizing Otitis Externa; Skull Base Osteomyelitis)

By

Bradley W. Kesser

, MD, University of Virginia School of Medicine

Last full review/revision Sep 2020| Content last modified Sep 2020
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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 by malignant external otitis. The osteomyelitis spreads along the base of the skull and may cause cranial neuropathies Overview of Neuro-ophthalmologic and Cranial Nerve Disorders Dysfunction of certain cranial nerves may affect the eye, pupil, optic nerve, or extraocular muscles and their nerves; thus, they can be considered cranial nerve disorders, neuro-ophthalmologic... read more (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 Staphylococci are gram-positive aerobic organisms. Staphylococcus aureus is the most pathogenic; it typically causes skin infections and sometimes pneumonia, endocarditis, and osteomyelitis... read more ) 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

  • CT scan of the temporal bone

  • Biopsy

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 Squamous Cell Carcinoma Squamous cell carcinoma is a malignant tumor of epidermal keratinocytes that invades the dermis; this cancer usually occurs in sun-exposed areas. Local destruction may be extensive, and metastases... read more Squamous Cell Carcinoma ).

Treatment of Malignant External Otitis

  • Systemic antibiotics, typically a fluoroquinolone and/or an aminoglycoside/semisynthetic penicillin combination

  • Topical antibiotic/corticosteroid preparations (eg, ciprofloxacin/dexamethasone)

  • Rarely, surgical debridement

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.

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