Dermatology Made Easy is based on the most popular topics from DermNet NZ's vast array of material. The book combines the essential focus of the ‘Made Easy’ book series with the authority and knowledge base of DermNet NZ's unparalleled resources.
Author: Vanessa Ngan, Staff Writer, 2005.
Otitis externa is an inflammatory condition of the external auditory canal (the ear canal). It is characterised by redness, swelling, scaling and thickening of the canal skin lining and is accompanied by varying degrees of discomfort, itch, deafness and discharge.
The causes of otitis externa can be split into two main groups: those caused by bacterial or fungal infection and those by non-infectious dermatological conditions. Bacterial infections are the most common cause of otitis externa. Primary skin disorders are often precipitants of infectious otitis externa, but they can also be the sole cause of otitis externa.
As with all skin the external auditory canal has a normal bacterial flora that remains free from infection until skin defences fail or become damaged. Some common causes that allow the overgrowth of bacteria in the external ear include:
Bacteria commonly implicated in otitis externa include Pseudomonas aeruginosa and Staphylococcus aureus. In about 10% of cases of infectious otitis externa, fungal infections are the cause. The most common fungal pathogen is Aspergillus (80-90%), followed by Candida. Mixed bacterial and fungal infections are common.
Otitis externa caused by dermatological conditions are often referred to as “eczematous otitis externa”. Skin conditions that may cause otitis externa include:
Often the condition is complicated by secondary bacterial infections.
The most common symptoms of otitis externa are otalgia (ear discomfort) and otorrhoea (discharge from the external auditory canal). Ear discomfort can range from pruritus (itching) to severe pain that is worsened by motion of the ear, e.g. chewing. Discharge from the ear varies between patients and may give a clue to the cause of the condition. Swelling within the external auditory canal may cause feeling of fullness in the ear and loss of hearing. The clinical features of otitis externa may vary according to the cause.
Allergic contact dermatitis
Irritant contact dermatitis
History taking and physical examination is often all that is required to make a diagnosis of otitis externa. If fever or signs of toxicity are present, perform standard laboratory testing. Gram staining and culture of the discharge may be helpful, particularly when a bacterial or fungal cause is suspected.
Initial treatment begins with cleaning debris and wax from the canal. Once the ear is cleaned specific treatment that is prescribed according to the cause of otitis externa should be administered. Occasionally if swelling in the ear is severe, a wick may be inserted before medication is applied, usually in the form of topical eardrops.
Systemic dermatological disease, e.g. psoriasis
Patients should be educated about how to prevent recurrences of otitis externa. Some simple general measures include:
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