Otitis externa (OE), also referred to as external otitis, is inflammation of the auricle, external ear, or tympanic membrane. The severity can range from mild inflammation to life-threatening infection. It is commonly seen by family physicians and affects 4 out of each 1000 Americans every year. In most cases the significant pain of OE compels the patient to seek care urgently.
OE can be categorized as localized or diffuse. When it persists for more than 6 months, it is considered chronic and is more commonly bilateral. It is thought to be caused by local trauma to the external canal, diabetes, high humidity, loss of the canal's protective coating of cerumen, eczema, use of a hearing aid or stethoscope, or glandular obstruction. It is commonly seen in swimmers, particularly in the summer months. The most frequent symptoms are discharge, pain, hearing loss, itching, and tinnitus.
Necrotizing (malignant) otitis externa (NOE) is the most severe form of OE and is most often seen in elderly patients with diabetes. One case series in a referral population found a mortality rate of 53%. Pain, purulent discharge, bilateral involvement, and external canal granulation tissue are common symptoms.
KEY WORDS Otitis externa; ear canal; infection. (J Fam Pract 2001; 50:353-360)
* Otitis externa (OE) is a clinical diagnosis. Diagnostic testing is not necessary.
* The combination of ear cleaning, ear wicks, and topical medications is most effective for the treatment of OE. Use of a single topical intervention or oral antibiotics may be effective but is less well supported.
* Necrotizing otitis externa (NOE) is also a clinical diagnosis that is based on poor response to treatment and the presence of granulation tissue. It is more common in persons with diabetes, especially older patients.
* Ear cleaning, debridement, and oral ofloxacin or ciprofloxacin for up to 3 months are the preferred treatment for NOE.
The ear canal is a blind sac with an anterior recess. Trauma to the canal, accumulation of keratin, or a change in pH can trigger inflammation and infection. One study found that aerobic bacteria account for 91% of bacterial causes; anaerobes, 4%; and mixed infections, 4%. The most common offending organisms are Pseudomonas aeruginosa (50%), Staphylococcus aureus (23%), anaerobes and gramnegative organisms (12.5%), and yeast, such as Aspergillus and Candida (12.5%). The increased pH of pool water is believed to make infection more likely, since bacteriologic studies fail to show a direct link between swimming pool contamination and the organisms of OE.
There are no published studies of the accuracy of the medical history, physical examination, or office laboratory tests for the diagnosis of OE. Diagnosis is usually made based on physical examination findings: pain on movement of the auricle, edema, redness, and foul-smelling discharge. Swelling often obscures the tympanic membrane.
NOE is also a clinical diagnosis and requires a high index of suspicion. A study by Zaky and colleagues considered 2 new cases and 32 that were retrospectively reviewed from the literature. They found the following frequencies of symptoms: pain (100%0), purulent discharge (97%), bilateral involvement (21%), and a polyp in the external canal (88%). Diabetes was common in this group of patients (82%), confirming that it is consistently a predisposing risk factor, and 91% of these patients were aged 55 years and older.
Few papers have been published concerning diagnostic studies for NOE. One found that temporal radiographs and tomograms are positive in most cases of NOE but were not necessary for diagnosis. The erythrocyte sedimentation rate is usually increased, but this is true in many other illnesses. Many studies[3,8-9,31-35] have reported that Pseudomonas is the primary offending organism for NOE. Because most ear cultures are positive for Pseudomonas, these cultures are of questionable value.
There are 4 studies that consider more aggressive diagnostic testing for NOE using conventional temporal radiographs, tomographic temporal radiographs, qualitative and single photon emission computed tomography gallium scans, and qualitative and quantitative technetium bone scans.[6-9] These studies were limited by the use of unclear or poor quality[6,8] reference standards (radiograph or poor response to antibiotics). The diagnosis of NOE does not require additional studies. Expert opinion supports a diagnosis based on the history and physical examination and poor response to treatment. The most common symptom of NOE is persistent pain that is constant and severe. The leukocyte count may be normal or mildly elevated. Physicians should consider the diagnosis of NOE in any patient with diabetes who has OE, particularly older patients. Characteristics of OE and NOE are presented in Table 1.
The main principles of treatment are local cleansing of debris, drainage of the infection, re-establishment of the normal acidic environment, use of topical and systemic antimicrobials, and prevention of recurrent infections. The evidence regarding these treatments is summarized in Table 2. The best evidence (grade of evidence: A) demonstrates equivalent results with ear cleaning, an ear wick, and any of the choices of topical agents[12-13]--acidifying agents, antibiotics, antibiotic and steroid combinations, or antifungal agents. Frequent dosing (3 to 4 times daily) for at least 4 days is supported by the studies. Two studies demonstrated equivalent efficacy with topical ciprofloxacin or ofloxacin dosed twice daily compared with antibiotic and steroid combinations dosed 4 times daily.[16-17] However, these agents are also more expensive than older topical antibiotics. The evidence for single topical treatments and oral antibiotics is weaker[14-29] (grade of evidence: B). Physicians should treat patients with one of the following regimens for at least 4 days:
* ear cleaning + ear wick + acidifying agent dosed 4 times daily
* ear cleaning + ear wick + topical antibiotic dosed 4 times daily (twice daily if quinolone)
* ear cleaning + ear wick + topical antibiotic/steroid combination dosed 4 times daily (twice daily if quinolone)
The ear is best cleaned by simply irrigating the canal. Be sure to look for a foreign body, particularly in younger patients. For a wick, use either the Pope ear wick (Merocel Corporation, Mystic, Conn) or a fourth-inch sterile gauze. The wick helps draw topical medications into the affected canal, particularly when it is obstructed. The patient should return in approximately 2 days for removal of the wick and reassessment. Do not forget analgesics; this is a painful condition.
NECROTIZING OTITIS EXTERNA
The treatment for NOE must be aggressive. As the infection invades through the soft tissues into surrounding bony structures, it can be life threatening. The evidence for various treatments is presented in Table 3. The studies are weaker than those for treatment of otitis externa (grade of recommendations: B and C). They support twice daily dosing with oral ofloxacin 400 mg orally twice daily or ciprofloxacin 750 mg orally twice daily for up to 3 months.[31-33] There is weak evidence that hyperbaric oxygen is effective. Intravenous anti-Pseudomonal antibiotics are often used initially, based on expert opinion (grade: D) and the high mortality rate.
The oral fluoroquinolones (ofloxacin and ciprofloxacin) show promise for treating NOE. The choice of parenteral or oral antibiotics still rests with clinician judgment, based on the patient's clinical presentation. If oral antibiotics are started, the length of treatment should be based on the severity of illness.
The prognosis for cure of OE is excellent, although the actual natural history of untreated disease has not been studied. OE complicated by NEO is more common in persons with diabetes who have a persistent course and granulation tissue visualized in the external auditory canal. Untreated NEO can lead to osteomyelitis and paralysis of cranial nerves. Death can result from sepsis and central nervous system infection.
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* Submitted, revised, March 4, 2001.
From the Clinton Memorial Hospital Family Practice Residency, Wilmington, and the University of Cincinnati Department of Family Medicine. Reprint requests should be addressed to Keith B. Holten, MD, Family Health Center, 825 W. Locust St, Wilmington, OH 45177. E-mail: firstname.lastname@example.org.
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