Otitis externa is an infection of the external ear that is commonly seen in primary care.
With a prevalence of around 1%, it is more common in younger people and women. The incidence is higher in hot, humid climates and near the end of summer.
We will look at the causes, clinical features, and treatment of otitis externa in this article.
Pathophysiology
Otitis externa most commonly affects the external auditory canal, which is the part of the ear through which sound waves travel to reach the tympanic membrane.
Any disruption in wax formation (e.g., repeated water exposure), canal trauma (e.g., cotton buds), or blockage (e.g., debris) can compromise the external auditory canal’s protective mechanisms, resulting in pathogen overgrowth and inflammation.
The skin becomes erythematous, swollen, tender, and warm, resulting in the accumulation of debris and discharge. The narrowing of the canal, combined with debris accumulation, leads to further pathogen entrapment and the spread of the infectious process.
Pseudomonas Aeruginosa (around 40%), S. Epidermidis, S. Aureus, and anaerobes are the most common pathogens. It can also be caused by a fungal infection (typically Aspergillus spp.) in rare cases.
The Risk Factors
The main risk factors for otitis externa are those that interfere with the external auditory canal’s normal protective mechanisms:
- Water contact on a regular basis (e.g., swimmers and frequent hair washers)
- Humid conditions
- Polyps or foreign bodies in the ear
- Ear canals that are too narrow
- Eczema or psoriasis of the ears
- Local trauma (for example, hearing aids or excessive cotton bud use)
- Patients who are predisposed to infection (such as the immunocompromised or diabetic) are more likely to develop otitis externa.
They are also more likely to develop complications (such as malignant otitis externa), so extra care must be taken when treating these patients.
Clinical Features
The classic clinical picture of otitis externa is progressive ear pain with purulent discharge (Fig. 2), as well as itchiness or ear fullness. Hearing loss, tinnitus, or describing a swollen ear are less common symptoms. Inquire about potential precipitants or risk factors for otitis externa.
The external ear canal will appear swollen and erythematous on examination. On palpation, the pinna and tragus may be swollen and tender. Any discharge is usually purulent, and the color may indicate the underlying cause:
- White-yellow – associated with bacterial infection
- Thick white grey with visible hyphae or spores – fungal infection
- Clear grey – otitis media
Diagnosis Differential
The following are important differentials to consider for anyone presenting with ear discharge:
- Otitis media with perforation – usually a clear or bloody discharge followed by pain relief, caused by an inflamed tympanic membrane with perforation.
- Ramsay Hunt syndrome – may present with otitis externa symptoms but has evidence of vesicular eruptions within 2 days of pain onset.
- Furuncle is a painful ear canal caused by the formation of a localised abscess caused by infection of the hair follicle in the lateral third of the ear canal. When using an otoscope, there is a visible bulge.
Ear canal malignancy, branchial cyst, atopic dermatitis, and exostosis are less common conditions.
Investigations
Otitis externa is typically a clinical diagnosis based on a thorough history and otoscope examination of the ear.
If antibiotics do not resolve otitis externa or there are signs of fungal disease on otoscopy, swabs of the discharge can be sent for culture. Checking glucose levels for diabetes mellitus may be useful in recurrent disease.
As discussed further below, any complicated cases of otitis externa may necessitate a High Resolution CT (HRCT) scan to determine the extent of the disease.
Management
Prevention, aural toileting, topical antibiotics, and simple analgesia are the mainstays of treatment for otitis externa.
Because no single topical antibiotic regimen has been found to be superior*, antibiotic selection is based on patient and doctor preference, local sensitivities, and adverse reactions.
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When there is evidence of canal inflammation, steroid drops have been shown to be beneficial. It works to reduce swelling (allowing the antibiotic to perforate) and pain.
*Oral antibiotics have not been shown to benefit uncomplicated otitis externa and should be avoided (unless cellulitis or pinna involvement is present).
Prevention
Microsuction should be used to remove any debris. Exacerbating factors, such as swimming, should be avoided by the patient. They should consider a bone-anchored hearing aid (BAHA) instead of a standard hearing aid. Any underlying eczema or polyps should be treated as needed.
Complications
Otitis externa is typically treated with topical antibiotics. However, in cases of delayed presentation, resistant organisms, or immunocompromised patients, the infection may progress to a more severe form.
Referral to an ENT specialist is required when the infection is severe, the patient develops complications, or has symptoms indicating middle/inner ear involvement.
Malignant otitis externa, mastoiditis, osteomyelitis, and intracranial spread are all possible complications of otitis externa.
Malignant otitis externa is a form of OE that extends into the mastoid and temporal bones. It usually affects elderly diabetics (or the immunocompromised), causing severe pain and headaches and necessitating an urgent CT scan. It can result in CN VII involvement and necessitates immediate debridement with IV antibiotics.
