OTITIS EXTERNA

Saturday, August 16, 2008

Essentials of Diagnosis

• Infection and inflammation of the external auditory canal causing pain and itching, similar to infections of the skin and soft tissue.

• S aureus or group A Streptococcus often causes acute localized otitis externa, similar to furunculosis.

• Main symptoms are localized pain and itching.

• "Swimmer's ear" or acute diffuse otitis externa is often caused by P aeruginosa or by Aspergillus spp.

• Chronic otitis externa results from persistent drainage caused by chronic suppurative otitis media. This may present as chronic itching.

• "Malignant" otitis externa is a severe necrotizing P aeruginosa infection of the external auditory canal and adjacent tissues. Severe pain, tenderness, and other signs of complications may be present.

General Considerations

Inflammation of the EAC is particularly symptomatic because of the limited space for expansion of edematous tissue in the narrow external auditory canal.

Clinical Findings

A. Signs and Symptoms. Infection of the EAC is divided into four different categories (Box 9-12):

1. Acute localized otitis externa is the most common form of otitis externa. It is similar to staphylococcal infections of the skin and hair follicles. Because of limited area for expansion, inflammation and edema of the EAC wall cause intense pain and tenderness. The canal has local erythema, heat, and tenderness over the tragus. There may be associated preauricular lymphadenopathy.

2. Acute diffuse otitis externa or "swimmer's ear" is caused mainly by gram-negative organisms, particularly P aeruginosa. It occurs in hot, humid climates or may be associated with contaminated hot-tub baths. Fungal organisms such as Aspergillus spp. may also cause symptoms of pain and itching in the ear. The canal is erythematous, edematous, and, in some severe cases, hemorrhagic.

3. Chronic otitis externa is a complication of persistent chronic otitis media and resultant drainage into the EAC leading to chronic irritation. Itching of the EAC is the main symptom.

4. "Malignant" or invasive otitis externa is a severe, necrotizing infection of the EAC with invasion into the surrounding tissues including blood vessels, cartilage, and bone. P aeruginosa is the most frequently isolated organism. Immunocompromised hosts, elderly, and particularly diabetics are predisposed to this disease

B. Laboratory Findings. Laboratory findings are not helpful in the diagnosis and management of otitis externa. The white blood cell count and sedimentation rate may be elevated in malignant otitis externa. Cultures from the EAC or involved tissue in malignant otitis externa are frequently positive for P aeruginosa or other bacteria.

C. Imaging. Imaging is not required for otitis externa but CT or magnetic resonance imaging of the head delineates the extent of damage in malignant otitis externa and its complications. This could potentially aid in the further management of this condition.

Complications

Complications develop by local invasion such as temporal bone osteomyelitis, septic thrombophlebitis of the sigmoid or lateral sinus or jugular bulb, cranial nerve palsies, meningitis, or brain abscess.

Treatment

Gentle cleaning is recommended for most otitis externa. Local heat, topical antibiotic solutions such as neomycin, polymyxin, or ofloxacin, or systemic antibiotics, or some combination of these are effective in the treatment of acute otitis externa (Box 9-13). Irrigation with hypertonic (3%) saline and cleansing with alcohol and acetic acid mixed 1:1 are recommended for acute diffuse otitis externa, whether it is bacterial or fungal. Fungal otitis externa may also be amenable to treatment with m-cresyl acetate. Topical antibiotics combined with steroids are sometimes used for 1-2 d to decrease edema. Severe infections may require systemic antibiotics with activity against P aeruginosa. Malignant otitis externa may be treated with parenteral antipseudomonal antibiotics such as ceftazidime or penicillins with antipseudomonal activity such as piperacillin with aminoglycoside or oral antipseudomonal antibiotics such as the fluoroquinolones. Topical antipseudomonal antibiotics, such as neomycin, polymyxin, or ofloxacin, are used for 4-6 wk.

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