Epidemiology

Research has shown otitis externa to be the diagnosis in approximately 1% of new GP consultations.^[1][2]

Risk factors

It is more common in hot and humid climates (or at the end of the British summer) and five times more common in swimmers. It is most frequently seen in the 45-75 year-old age group.

Aetiology

It may be infectious in origin or caused by allergies, irritants or inflammatory conditions.

Infections

These can take many forms:

• There may be an infected hair follicle when Staphylococcus aureus is the usual infecting organism. Infection is localised.
• In more general, infection of the outer ear may be bacterial (90%) or fungal (10%).^[3]
• Fungal infection usually follows prolonged treatment with antibiotics, with or without steroids. About 1 in 8 otitis external infections is fungal in origin. 90% of fungal infections involve Aspergillus spp. and the rest are Candida spp.
• Dermatophyte infection may occur and seborrhoeic dermatitis may be followed by infection with Malassezia spp.
• Herpes zoster (Ramsay Hunt syndrome).

Skin diseases

These include:

• Seborrhoeic dermatitis
• Acne
• Psoriasis
• Atopic eczema
• Systemic lupus erythematosus

Irritants

These include topical medications, hearing aids or earplugs:

• Aggravating or causative factors include ear trauma from foreign bodies in the ear, cotton buds, ear syringing or hearing aids. Swimmers are more susceptible, especially in polluted water. Chemicals including hair spray, hair dyes and cerumenolytics as well as various skin conditions may be responsible.

Presentation

The following may be a useful indicator of the most likely aetiology and hence the most appropriate treatment:

A furuncle

This is small with severe pain in the ear and local swelling of the canal. Pyrexia is moderate (less than 38°C). There may be posterior auricular lymphadenopathy. Examination with an auriscope can be very painful. If the lesion bursts there is sudden relief of pain.

Acute diffuse otitis externa

This produces a similar temperature and lymphadenopathy. Swelling is more diffuse and pain is variable with possible pruritus. Moving the ear or jaw is painful. The canal, external ear, or both, are red, swollen, or eczematous, with shedding of the scaly skin. There may be little, but thick, discharge in the acute stage but it can become bloody if chronic. Hearing is often impaired. Bacterial infection is common and may be secondary to skin disease, eg seborrhoeic dermatitis.

Chronic otitis externa

If due to infection this is usually due to fungal causes. More likely causes are underlying skin conditions - as below.

Superficial fungal infection

This tends to be chronic. Complaints are of itching and discomfort. Discharge is variable. See separate article Fungal Ear Infection for further detail.

Contact dermatitis

This can be irritant or allergic. Irritant is usually insidious in onset with lichenification. Allergic forms tend to be more rapid in onset with itching, erythema and oedema. If otitis externa persists despite conventional treatment, consider allergy, usually to an aminoglycoside. Patch testing may be required.^[4]

Other skin diseases

If seborrhoeic dermatitis or atopic dermatitis are involved there will be local evidence of that disease.

Necrotising or malignant otitis externa

This is rare but is a life-threatening extension of otitis externa into the mastoid and temporal bones. It is usually due to Pseudomonas aeruginosa or S. aureus. It usually affects elderly diabetics or those who are immunocompromised. It produces pain and headache of greater intensity than clinical signs would suggest. Facial nerve palsy is a red flag sign but is not necessarily associated with a poorer prognosis.^[5] Obligatory criteria for diagnosis include:^[6]

• Pain.
• Oedema.
• Exudate.
• Granulation tissue (may be present at the junction of bone and cartilage).
• Microabscess (when operated upon).
• Positive bone scan or failure of local treatment and possibly pseudomonas in culture.

The occasional criteria are:

• Diabetes
• Cranial nerve involvement
• Positive radiograph
• Debilitating condition
• Old age

A technetium ^99m Tc bone scan is very important. The typical patient is either an old person with diabetes or a young person with HIV but atypical patients are not uncommon and a high index of suspicion is required.^[7]

Investigations

Swabs are required only if there has been treatment failure or the situation looks atypical.

Differential diagnosis

• Foreign bodies may be present.
• Impacted wax can cause pain and deafness. Drops will make it swell and can aggravate it before removal.
• Otitis media is painful but, if the drum bursts, the pain ceases and a discharge follows.
• A chronic discharging ear is associated with chronic suppurative otitis media and possibly cholesteatoma.
• If the ear is swollen with a canal that bleeds readily on contact, consider malignancy.
• Pain can be referred from the sphenoidal sinus, teeth, neck, or throat.
• Barotrauma usually affects divers and, less commonly, those who have recently flown; however, it can result from a blow to the ear.
• Dermatological disease, as listed above.

Management

The aim of treatment is:

• To settle symptoms.
• To cure infection.
• To reduce risk of recurrence.
• To prevent complications.

If the condition is painful, then appropriate analgesia is required.

• Topical treatment is recommended, unless there is spread with cellulitis or the patient is systemically unwell. In most cases the choice of topical intervention does not appear to influence the therapeutic outcome significantly.^[8]
• A swollen ear canal should be packed with a wick or ribbon gauze soaked in steroid solution or an astringent to facilitate its passage along the ear canal.
• Otherwise, advise the patient to lie on one side with the affected ear up, to introduce the ear drops, and to keep this position for 10 minutes.
• Treatment with an an antibacterial or corticosteroid should be for no longer than seven days, because of risk of secondary fungal infection or possible allergy developing.
• Contact sensitivity with topically applied ear drops is most commonly due to antibiotics, especially aminoglycosides and preservatives.

Management for children is the same as for adults.

Acute otitis externa

Analgesia is usually required.

• The canal must be cleared of debris and discharge, as this lowers the pH and reduces the activity of aminoglycoside ear drops. This may be required several times a week.
  • If there is an irritant or allergen it must be removed.
  • Keep the ear dry and avoid scratching it with cotton wool buds.
  • Avoid cotton wool plugs in the ear unless discharge is so profuse that it is required for cosmetic reasons. If used, keep them loose and change often.
  • Avoid swimming or at least prevent water from entering the ear.
• Evidence of spreading infection or cellulitis requires oral antibiotics.
• The evidence for steroid-only drops is very limited and, as yet, not robust enough to allow us to reach a conclusion or provide recommendations.^[8]
• Acetic acid 2% eardrops can be very effective. They are available on prescription or over the counter as EarCalm®. They are effective against both bacterial and fungal infection. They are less likely to cause allergy than aminoglycosides and less likely than steroids are to cause superinfection but the acid does sting and this may impair compliance.
• Antibiotic drops usually contain aminoglycosides or fluoroquinolones and possibly an antifungal.^[9] Clioquinol is effective against both. They are often combined with steroid. Aminoglycoside drops may be contra-indicated if there is perforation of the eardrum, as they can be ototoxic.
• Advise patients to use the drops for at least a week. If the symptoms have not resolved by then, they should continue until they are better (and possibly for a few days afterwards), for a maximum of a further seven days.^[8] Patients whose symptoms last for more than two weeks should have an alternative plan started.

Chronic otitis externa

Chronic otitis externa occurs over months or years and there has often been modification of the normal flora by treatment. Topical medication is preferred.

• Try to identify the cause or aggravating factors, such as inadequate aural toilet, continued trauma from scratching or swimming:
  • Poor compliance with treatment or contact sensitivity to previous topical treatment can be a problem.
  • Excessive use of antibacterial drops can lead to fungal infection.
  • There may be skin disease.
  • Hearing aid, ear plugs, or anatomical problems, such as meatal stenosis, should be identified.
• General measures of hygiene apply.
• If no cause is apparent, prescribe seven days of acetic acid 2% ear drops together with corticosteroid ear drops. Treatment can be difficult and referral may be required.

Necrotising otitis externa

Necrotising or malignant otitis externa is caused by P. aeruginosa in 90% of cases.^[10] Oral and topical treatment, usually as quinolones, and given for 6 to 8 weeks, are usually required. Evolving resistance to ciprofloxacin can be a problem.^[11]

Choice of drug

For acute otitis externa, first choices for treatment include:

• For antibacterial cover: neomycin combined with betamethasone, hydrocortisone, prednisolone, or gentamicin on its own or combined with hydrocortisone. The addition of dexamethasone to polymyxin B/neomycin significantly reduces swelling and leads to significantly higher patient ratings of treatment efficacy.^[12]
• For antibacterial and antifungal cover: clioquinol plus flumetasone.

Oral antibiotics are indicated if the patient is systemically unwell or there is evidence of spreading infection.

• Flucloxacillin (or erythromycin if there is penicillin allergy) is preferred, because infection is usually due to S. aureus.

Complications

If initial therapy fails then reconsider diagnosis. If the patient develops cellulitis or cervical lymphadenopathy, oral antibiotics are necessary.

Malignant otitis externa may involve the mastoid and there may be facial nerve palsy.

Prognosis

Most cases of otitis externa resolve within a few days of starting treatment. If malignant otitis externa is suspected, urgent referral to ENT should be made.