Otitis Externa

Otitis externa is an infection of the external ear, a common condition that is mainly seen in primary care.

It is more common in younger ages and females, with a prevalence of around 1%. The incidence tends to be higher in hot and humid climates, and towards the end of summer.

In this article, we shall look at the causes, clinical features and management of otitis externa.

Pathophysiology

Otitis externa typically affects the external auditory canal – the part of the ear via which sound waves travel to reach the tympanic membrane.

Any interruption in wax formation (e.g. repeated water exposure), trauma to the canal (e.g. cotton buds) or blockage (e.g. debris) can disrupt the external auditory canal’s protective mechanisms, and lead to pathogen overgrowth and inflammation.

The skin becomes erythematous, swollen, tender, and warm, leading to debris and discharge accumulation. The narrowing of the canal, in combination with the accumulation of debris, leads to further entrapment of pathogens and propagating the infective process.

The most common causative pathogens are Pseudomonas Aeruginosa (around 40%), S. Epidermidis, S. Aureus, and anaerobes. In rarer cases, it can be due to a fungal infection (typically Aspergillus spp.).

By TeachMeSeries Ltd (2020)

Figure 1 – The surface of the external ear

Risk Factors

The main risk factors for otitis externa are those that interfere with the normal protective mechanisms of the external auditory canal:

• Frequent water contact (e.g. swimmers and frequent hair washers)
• Humid environments
• Presence of ear polyps or foreign bodies
• Narrow ear canals
• Ear eczema or psoriasis
• Local trauma (e.g. hearing aids or excessive use of cotton buds)

Patients predisposed to developing infections (e.g. immunocompromised or diabetics) are at increased risk of otitis externa.

They are also at a higher risk of complications (such as malignant otitis externa), therefore extra care must be taken when treating these individuals.

Clinical Features

The classical clinical picture of otitis externa is progressive ear pain with a purulent discharge (Fig. 2), alongside itchiness or ear fullness. Less common symptoms include hearing loss, tinnitus, or describing a swollen ear. Ensure to enquire about potential precipitants or risk factors for otitis externa.

On examination, the external ear canal will appear swollen and erythematous. The pinna may be swollen and the tragus may be tender on palpation. Any discharge is usually purulent; the colour of which may indicate the underlying cause:

• White-yellow – related to bacterial infection
• Thick white grey with visible hyphae or spores – fungal infection
• Clear grey – otitis media

By Klaus D. Peter CC BY 3.0], via Wikimedia Commons

Figure 2 – Otitis Externa affecting a patient’s left ear

Differential Diagnosis

Important differentials to consider for anyone presenting with ear discharge include:

• Otitis media with perforation – usually clear discharge or bloody followed by relief of pain, with an inflamed tympanic membrane with perforation.
• Ramsay Hunt syndrome – may present with symptoms of otitis externa, yet has evidence of vesicular eruptions within 2 days of first onset of pain.
• Furuncle – a painful ear canal due to localised abscess formation from infection of the hair follicle in the lateral third of ear canal. A visible bulge is present when examining with an otoscope.

Less common conditions include ear canal malignancy, branchial cyst, atopic dermatitis, and exostosis.

Investigations

Otitis externa is usually a clinical diagnosis, based on a thorough history and examination of the ear using an otoscope.

If otitis externa is not resolving with antibiotics or there are signs of fungal disease on otoscopy, swabs of the discharge can be sent for culture. In recurrent disease, it may be useful to check glucose levels for diabetes mellitus.

As discussed later, any complicated cases of otitis externa may warrant a High Resolution CT (HRCT) scan to investigate the extent of the disease.

Management

The mainstay of management in otitis externa involves prevention, aural toileting, topical antibiotics, and simple analgesia.

No single topical antibiotic regime has been found to be superior*, thus the antibiotic choice depends on the patient and doctor preference, local sensitivities and adverse reactions.

Steroid drops have been shown to be beneficial when there is evidence of canal inflammation. It acts to decrease the swelling (allowing the antibiotic to perforate) and reduce pain.

*Oral antibiotics have not been shown to offer any benefit in uncomplicated otitis externa and are usually avoided (unless evidence of cellulitis or pinna involvement)

Prevention

Any debris present should be removed by microsuction. The patient should be advised to avoid exacerbating factors, such as swimming. If using a standard hearing aid, they should consider a bone-anchored hearing aid (BAHA) instead. Any underlying eczema or polyps should be managed appropriately.

Complications

Otitis externa usually resolves with topical antibiotics. However, in cases of delayed presentation, resistant organism or immunocompromised patient, it may extend to a more severe infection.

When the infection is longstanding, the patient develops complications, or has symptoms suggesting middle/inner ear involvement, referral to an ENT specialist is required.

Potential complications of otitis externa include malignant otitis externa, mastoiditis, osteomyelitis, and intracranial spread.

Malignant otitis externa is an extension of OE into the mastoid and temporal bones. It typically occurs in the elderly diabetics (or immunocompromised), presents with severe pain and headaches, requiring an urgent CT scan. It can cause CN VII involvement and requires urgent debridement with IV antibiotics.