The external ear is subject to a wide variety of pathology. This article will focus on acute otitis externa (inflammation of the outer ear canal), with an emphasis on diagnosis, treatment and warning signs of more sinister pathology.
Acute otitis externa (AOE) is usually infectious in nature. It is more common in warm, humid environments, with about 80% of cases occurring during summer.
The condition is thought to result from a loss of integrity of the hydrophobic, acidic, ceruminous layer of the external auditory canal. This exposes the epithelium of the canal to water and bacterial infection. Infection leads to an inflammatory response causing erythema and oedema of the epithelium, with resulting otalgia, pruritus and jaw pain. If oedema is severe, hearing loss may result from occlusion of the canal.
Other factors that may predispose a person to AOE include anatomical obstructions such as exostoses (see figure 1), impacted cerumen or canal stenosis. The use of hearing aids, earplugs, or cotton ear buds may also predispose to infection. Water exposure is a significant risk factor and the condition is sometimes referred to as swimmer’s ear. Immunosuppressed patients, including those with diabetes mellitus, AIDS or undergoing chemotherapy, are at greater risk of developing AOE and its complications.
The most commonly cultured organisms are Pseudomonas aeruginosa, Staphylococcus epidermis and Staphylococcus aureus. Fungal AOE is less common and accounts for 1-10% of cases. Fungal otitis externa may, however, occur as an opportunistic infection following treatment for bacterial AOE. Patients with fungal otitis externa may complain more of pruritus than pain.
Otalgia in AOE may be severe and is often exacerbated by manipulation of the ear. Associated symptoms include itching, hearing loss and jaw pain. The external auditory canal will often be erythematous and oedematous. In the case of suspected fungal otitis externa, the canal should also be inspected for the presence of fungal hyphae (see figure 2).
There may be otorrhoea in the canal and the tympanic membrane may not be visible due to oedema. If the tympanic membrane can be visualised, it should be assessed for possible perforation or the presence of a ventilation tube (grommet).
An episode of AOE can be secondary to acute otitis media, and ototoxic topical drops should be avoided in the presence of these.