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.1 It is commonly seen by family physicians and affects 4 out of each 1000 Americans every year.2 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.1 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%.3 Pain, purulent discharge, bilateral involvement, and external canal granulation tissue are common symptoms.
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 study4 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 gram-negative 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.5 Swelling often obscures the tympanic membrane.
NOE is also a clinical diagnosis and requires a high index of suspicion. A study by Zaky and colleagues3 considered 2 new cases and 32 that were retrospectively reviewed from the literature. They found the following frequencies of symptoms: pain (100%), 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.6 The erythrocyte sedimentation rate is usually increased,3 but this is true in many other illnesses. Many studies3,8-9,31-35 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.10
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 tomography67 gallium scans, and qualitative and quantitative99 technetium bone scans.6-9 These studies were limited by the use of unclear7 or poor quality6,8 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.3 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 agents12-13—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 weaker14-29 (grade of evidence: B).