What is otitis externa?
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.
What causes otitis externa?
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.
Infectious 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:
- Swimming, perspiration, high humidity – these create excessive moisture that carry bacteria into the cerumen (ear wax) of the ear canal, leading to maceration and inflammation
- Local trauma to the ear canal allowing bacteria to enter damaged skin, e.g. insertion of objects such as cotton buds, matchsticks and fingers to relieve itching or impacted earwax
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.
Non-infectious dermatological causes
Otitis externa caused by dermatological conditions are often referred to as “eczematous otitis externa”. Skin conditions that may cause otitis externa include:
- Atopic dermatitis (eczema)
- Seborrhoeic dermatitis
- Cutaneous lupus erythematosus (rare)
- Irritant or allergic contact dermatitis – from local irritants, including topical preparations or use of hearing aids or ear plugs
Often the condition is complicated by secondary bacterial infections.
What are the signs and symptoms?
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.
- Significant swelling of canal is common
- Discomfort is often severe enough to require oral analgesics
- Fever may be present
- Lymphadenopathy (swollen lymph nodes) around the base of the ear
- Discharge is usually scant white mucus, but occasionally thick in acute infection
- Bloody discharge in the presence of granulation tissue in chronic infection
- Often there are no symptoms apart from a discharge, this is typically a fluffy white to off-white discharge, but may be black, grey, bluish-green or yellow
- If symptoms are present, discomfort in the form of pruritus and a feeling of fullness in the ear is most common. Pruritus may be quite intense, resulting in scratching and further damage to the skin lining
- Tinnitus (ringing in the ears)
- Intensely itchy
- Typically part of a more generalised skin involvement, including the external ears, face and neck
- Skin may become red, thickened, crusty and hyperpgimented from scratching intense itch
- Commonly associated with scalp involvement but rarely facial involvement
- Raised, red lesion with thick, silvery-white adherent scale
- Often itchy
Allergic contact dermatitis
- Occurs suddenly
- Red, swollen, itchy and exuding lesions
- External auditory canal may react to allergens that do not cause a reaction elsewhere
- May affect the outer ear and lobe
Irritant contact dermatitis
- Slower onset than allergic contact dermatitis
- Lesions are usually patches of thickened, hardened skin
- May affect the outer ear and lobe
How is the diagnosis made?
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.
What treatment is available?
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.
- 2% acetic acid solution – inexpensive and effective against most infections but can be irritating to inflamed canal
- Neomycin otic drops – effective but can cause contact dermatitis in 15% of patients
- Polymixin B drops – avoids potential neomycin sensitisation but is ineffective against Staphylococcus and other gram-positive organisms
- Aminoglycoside drops – less irritating than previous preparations but has potential ototoxicity
- Fluoroquinolone drops (ofloxacin, ciprofloxacin) – very effective without causing irritation or sensitisation, no risk of ototoxicity, but is expensive and overuse may cause antibiotic resistance in an important class of antibiotics
- Topical drops that combine antibiotic with steroids may help to reduce inflammation and help resolve symptoms more quickly
- Drops are usually administered 3-4 times daily (fluoroquinolones only require twice daily administration) for 5-7 days. More severe infections may require 10-14 days treatment. Drops should be continued for 3 days more after symptoms disappear.
- Oral antibiotics are rarely indicated except for in severe and persistent otitis externa
- 2% acetic acid solution 3-4 times daily for 5-7 days
- If the infection does not respond to acidifying drops, antifungal drop such as clotrimazole can be used
- Aspergillus infections may be resistant to clotrimazole and require oral itraconazole
Systemic dermatological disease, e.g. psoriasis
- Goal of treatment should be to control the systemic dermatological disease
- Because these conditions are often inflammatory, topical steroid drops may be used but this can often lead to bacterial or fungal superinfection. Acidifying drop may be added to prevent secondary infection.
- Remove the irritant or allergen
- Topical steroids may be useful
- Burow's otic solution (aqueous solution of aluminium acetate) with 2% acetic acid may be added to prevent secondary infections, reacidify the skin, dry weeping lesions and remove crusts.
Patients should be educated about how to prevent recurrences of otitis externa. Some simple general measures include:
- Wear a tight fitting swimming cap to prevent water entering the ear canal
- Attention to drying the ears after swimming or showering
- Patients prone to recurrences may use acidifying drops after swimming or water sports
- Avoid poking and scratching the skin of the external auditory canal as damage to the skin and removal of earwax makes the canal more vulnerable to infection
- Patients with otitis externa should preferably abstain from water sports for at least 7-10 days.