External otitis is a diffuse inflammation of the skin of the ear canal causing pain, itching, discharge, scaling, redness or swelling and may be accompanied by hearing loss. The aetiology and pathophysiology are not entirely clear, but it appears that a disrupted acidic environment of the ear canal alters the local microbial flora and leads to inflammation. Normally, the lipidic and acidic characteristics of cerumen have a protective and bactericidal effect in the ear canal.
Acute external otitis is most common in summer. Swimming and other forms of water exposure are well-known risk factors. Other external factors are soap and shampoo, altering the pH of the ear canal. Furthermore, occlusion of the ear – for example, through the use of earplugs, hearing aids or earphones – increases ear canal moisture and irritation. It is assumed that picking at the ear and ear cleaning can lead to external otitis by removing cerumen and causing skin abrasions. A narrow ear canal is considered a further predisposing factor.
P. aeruginosa is the most common pathogenic micro-organism causing external otitis. This bacterium is sensitive to acidifying therapy. In <10% of patients with otitis externa, ear culture samples show the presence of a fungus, like Aspergillus or Candida albicans. This is more common in patients using hearing aids. In the absence of a causative micro-organism, a contact allergy, psoriasis or eczema may have contributed to the development of external otitis.
Diagnosis is based on history and physical examination. The distinction from acute otitis media with tympanic membrane rupture can sometimes be difficult.
Treatment consists of cleansing the ear canal from debris in the first place. This promotes healing in itself and is necessary for medication therapy to be effective. Cleansing is followed by the prescription of acid ear drops containing corticosteroids. If the tympanic membrane is not intact, aluminium acetotartrate ear drops should be prescribed. An ear wick drenched in ear drops can help decongest a swollen ear canal. Cleansing again and continued treatment are indicated if improvement does not occur after one (or two) weeks. A bacterial culture with resistance determination is advised when treatment fails after three weeks. Patients should be educated about external factors that may elicit external otitis. Systemic antibiotics are only indicated in case of fever and general illness. Analgesics can be used if necessary.
The prognosis of acute external otitis is good: more than 75% of patients are free of symptoms after three weeks of treatment.