Otitis Externa

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1.1. Epidemiology and Clinical Relevance

Otitis externa, an inflammatory condition involving the superficial layer of the external auditory canal, may be acute or chronic. Acute otitis externa in the elderly is generally a benign disorder, which may be localized or generalized. Chronic otitis externa is caused by the irritation due to the drainage from the middle ear in patients with chronic suppurative otitis media. An uncommon form of external otitis called "malignant otitis externa" is an invasive, necrotizing infection that spreads from the squamous epithelium of the ear canal to the periauricular soft tissue, blood vessels, cartilage, and bone (1-3).

Otitis externa is observed in the summer months more frequently, as the maceration of the skin lining the externa auditory meatus is facilitated by heat, humidity, and perspiration. Swimming may lead to otitis externa (swimmer's ear) by introducing moisture into the ear canal. Malignant otitis externa is typically seen in elderly diabetics in whom chronic hyperglycemia, tissue hypoperfusion due to microangiopathy, altered cell-mediated immunity, and impaired phagocytic function all play a pathogenetic role. Occasionally, malignant otitis externa has been noted after the syringing of the ear canal (4) and in patients infected with human immunodeficiency virus (HIV) (5). Complications that may be life threatening could result from the spread to the temporal bone, sigmoid sinus, jugular bulb, base of the skull, meninges, and the brain.

Otitis externa is generally caused by organisms such as Staphylococcus aureus and Pseudomonas aeruginosa. Malignant otitis externa is almost always due to P. aeruginosa (see Table 1). Only rare cases of malignant otitis externa due to S. aureus (6), Proteus mirabilis (7), and Aspergillus fumigatus (8) have been reported. Rare causes of chronic otitis externa include tuberculosis, fungal infections, syphilis, yaws, leprosy, and sarcoidosis. Fungal otitis externa may be part of a general or local fungal infection; Aspergillus spp. are responsible for the most cases (9).

1.2. Clinical Manifestations

Acute otitis externa causes pain in the ear that may be quite severe due to the limited space for expansion of the inflamed tissue. The movement of the external ear and sometimes of the jaw aggravates the pain. The patients may experience itching of the

From: Infectious Disease in the Aging Edited by: Thomas T. Yoshikawa and Dean C. Norman © Humana Press Inc., Totowa, NJ

Table 1

Salient Features of Malignant Otitis Externa in the Elderly

Predisposing factors Diabetes mellitus

Immunocompromise

Usually due to P. aeruginosa

Cranial nerve palsies (facial, glossopharyngeal, vagus, spinal accessory, hypoglossal, abducens, and trigeminal) Jugular venous thrombosis Cavernous sinus thrombosis Meningitis

Aminoglycoside + antipseudomonal penicillin (piperacillin, ticarcillin etc.) OR Aminoglycoside + ceftazidime OR Quinolones: ciprofloxacin, ofloxacin ear. The infection typically starts at the junction of the cartilage and bone in the external meatus. Speculum examination of the canal reveals the skin to be edematous and erythematous. There may be an accumulation of moist debris in the canal. The tympanic membrane may be difficult to visualize and may be mildly inflamed but is normally movable on insufflation. Acute localized otitis externa may occur as a pustule or furuncle associated with the hair follicles; S. aureus is generally the causative organism in these patients. Infection due to group A streptococcus may cause erysipelas of the concha and the canal. Examination may reveal hemorrhagic bullae in the ear canal or on the tympanic membrane, and regional lymphadenopathy may be noted.

Most episodes of otitis externa in the elderly resolve completely within 5-7 d. Failure of resolution of otitis externa should lead to suspicion of malignant otitis externa especially in elderly diabetics. Such patients have unremitting otalgia, tenderness of the tissues around the ear and mastoid, and purulent drainage from the canal. Examination of the ear canal reveals granulation tissue at the osseous-cartilaginous junction. The progression of malignant otitis externa along Santorini's fissure into the mastoid may lead to facial nerve palsy. The infection may further spread to the jugular foramen at the base of skull and involve the glossopharyngeal, vagus, and spinal accessory nerves. Similarly, extension of infection into the hypoglossal canal may involve the hypoglossal nerve, and involvement of the petrous apex may lead to the abducens and trigeminal nerves palsies. Other potential complications of malignant otitis externa include jugular venous thrombosis, cavernous sinus thrombosis, and meningitis.

1.3. Diagnostic Tests

The white blood cell count may be elevated in acute otitis externa, but this finding is nonspecific. The erythrocyte sedimentation rate is usually very high in patients with malignant otitis externa and may be useful in monitoring therapy (10). Cultures from

Microbiology Complications

Therapy the granulation tissue or the involved bone will reveal the organism. Plain film radiography is inadequate for the evaluation of malignant otitis externa. The extent of damage to the soft tissue and bone may be identified and monitored by use of computed tomographic (CT) and magnetic resonance image (MRI) scans (3,11). Technetium 99 bone scans and gallium 67 scans are very sensitive but not very specific (12,13). Bone scans may remain positive long after the microbiologic cure of this condition and therefore are not very useful in monitoring the response to therapy.

1.4. Therapy

The therapy of otitis externa consists of the gentle cleansing of the external auditory canal to remove debris and the instillation of appropriate topical antibiotics (14). The ear canal may be irrigated with hypertonic saline (3%) or cleansed with mixtures of alcohol (70-95%) and acetic acid. Inflammation of the canal may be reduced with hydrophilic solutions such as 50% Burrow solution. Eardrops of topical antibiotics (including neomycin and polymyxin), combined with a corticosteroid preparation, diminish the local inflammation. The placement of a wick in the ear canal may facilitate the delivery of antibiotic drops into the ear canal. Incision and drainage of the furuncle may be necessary to relieve severe pain. Systemic antibiotic therapy is reserved for significant tissue infection and systemic toxicity. Malignant otitis externa is treated with local debridement of the canal and topical treatment with antipseudomonal antibiotics combined with corticosteroids. Additionally, systemic therapy directed at P. aeruginosa should be used for 4-6 wk. The combination of a ceftazidime or an antipseudomonal penicillin (ticarcillin or piperacillin) with an aminoglycoside (gentamicin or tobramycin) should be considered for synergy. Oral quinolones with activity against P. aeruginosa, such as ciprofloxacin and ofloxacin, are also generally effective (15-18). Some consider ciprofloxacin to be the drug of choice due to its high concentration in the bone and cartilage, ease of oral administration, and low toxicity (19).

1.5. Prevention

Prevention of excessive moisture in the ear canal may favorably impact on the incidence of otitis externa. Use of a blow dryer after swimming to dry the ear canal has been suggested as a preventive measure. Aggressive cleansing of the ear canal should be avoided as the resulting disruption of its lining and subsequent invasion by resident bacterial flora may lead to infection. Prompt recognition of malignant otitis externa and its aggressive therapy will minimize its devastating complications.

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