The outer ear extends from clearly visible pinna (auricle) to the ear canal (external auditory canal) and ends at the ear drum (tympanic membrane). The outer ear focuses sound waves onto the eardrum which then vibrates. After transmission of these vibrations through the middle ear and stimulation of the hearing apparatus in the inner ear, the signals can then be perceived by the brain as sound.
The outer ear, however, is constantly exposed to the external environment and therefore prone to many of the same insults as other surface structures of the body. To reduce the impact on the eardrum, the opening of the ear canal is partly blocked by a small cartilaginous flap known as the tragus. The ear canal points downwards and is lined with epithelium that produces a sticky wax (cerumen), all of which contribute to protecting the integrity of the ear canal and eardrum. When these protective mechanisms are disturbed for any reason, the outer ear becomes prone to invasion by microorganisms.
What is Otitis Externa?
Otitis externa is a term used for inflammation of the outer ear but more specifically indicates an infection of the ear canal. Most of these infections are bacterial in origin although chronic cases may be due to fungi. The infection may be localized and present as a small furuncle (boil) or may be diffuse extending most of the length of the canal. Otitis externa is also commonly known as swimmer’s ear because of the frequency of these infections in people who swim on a regular basis. Unlike otitis media (middle ear infection) it can resolve quickly, sometimes even without medical treatment and serious complications are rare. However, in patients who are immunocompromised, otitis externa most can rapidly progress to result in serious and even life-threatening complications – malignant otitis externa.
How does otitis externa occur?
Infection of the ear canal is largely associated with disturbances in the microenvironment within the ear which is slightly acidic. It mostly revolves around any disturbance in the quantity of ear wax (cerumen) in the canal. Ear wax has a protective function, it is bitter tasting and acidic. It detracts insects from settling in the ear canal and has antimicrobial properties that prevents bacterial invasion.
Most cases are due to excessive cleaning of the ear with cotton swabs (ear buds), matchsticks, hairpins and other long objects. Apart from clearing out most of the ear wax, these makeshift instruments also injure the lining of the inner ear. Another common mechanism is with regards to swimming, particularly when water is trapped in the inner ear, thereby creating an ideal environment for bacterial invasion. This is further exacerbated by water contaminated with high levels of bacteria and chlorinated water in swimming pools which has an excessive drying effect on the lining of the ear canal.
Other factors, particularly underlying skin diseases, may also compromise the ability of the canal lining to maintain the acidic microenvironment. Apart from trauma to the ear canal, the bacteria that infect the canal leads to inflammation that is usually limited to the ear canal and superficial tissue. It rarely extends to deeper lying tissue.
Acute and Chronic Otitis Externa
Most infections are acute in nature and caused by a bacterial infection. It is associated with trauma, water in the ear and sometimes allergic reactions to soaps, shampoos, hair dyes and ear jewelry. Bacteria can quickly invade the irritated tissue. Acute infections typically lasts for 2 weeks and often the symptoms prompt the patient to seek medical treatment as soon as possible. Early treatment can therefore drastically reduce the duration of the infection. Chronic otitis externa typically lasts for more than four weeks (persistent) or may occur as more than four acute episodes in a period of one year (recurrent). Excessive clearing of the ear wax and dryness of the canal lining, coupled with moisture in the canal, allows for a fungal infection (otomycosis) with acute exacerbations due to a superimposed bacterial infection.
Malignant Otitis Externa
Malignant otitis externa (MOE) is an infection of the ear canal that extends to the deeper lying tissue including the temporal bone of the skull (osteomyelitis). The main causative organism is Pseudomonas aeruginosa, which is the same as in acute otitis externa. However, usually in uncomplicated otitis externa the infection is limited to the superficial layers of the ear canal. Malignant otitis externa is uncommon and almost entirely seen in immunocompromised patients, as is the case with poorly controlled diabetes mellitus, HIV/AIDS or patients on medication that suppresses the immune system. Apart from the typical symptoms of otitis externa described below, there is also prominent temporal headaches and facial nerve dysfunction.
Causes of Otitis Externa
The most common causes of a bacterial infection of the ear canal is due to the following species :
- Pseudomonas aeurginosa
- Staphylococcus aureus
- Proteus vulgaris
- Escherichia coli
Although rare, fungal infections of the ear canal (otomycosis) may be due to :
- Aspergillus niger
- Candida albicans
Various skin diseases can causes non-infectious inflammation of the ear canal (eczematous otitis externa). There is a higher risk of infections setting in due to disturbances in the microenvironment and compromised skin integrity. The more common skin diseases include :
- Atopic dermatitis
- Seborrheic dermatitis
- Contact dermatitis
Inflammation may also arise with topical medication in an otherwise healthy ear canal.
- Frequent cleaning the ears of ear wax
- Use of sharp or hard objects to ‘clean’ or scratch the ear canal
- Swimming, particularly in chlorinated water and contaminated water (bacteria)
- Certain shampoos, soaps, hair dyes and sprays that enter the ear canal
- Excess ear wax with debris lodged in the canal
- Objects that closely interact with the ear on a regular basis like headphones, hearing aids and ear plugs
- Narrow ear canal seen in children
Signs and Symptoms of Otitis Externa
Initially there is no pain or mild discomfort at most. Examination of the ear canal with an otoscope reveals a red, swollen canal that is slightly narrowed due to the inflammation. If a large furuncle is significantly occluding the ear canal, otoscopic examination may cause severe pain. Itching of the ear canal is often nagging (itchy ear) and there is small amounts of a clear odorless fluid commonly reported as ‘water in the ears‘. The entrance to the ear canal and tragus may be visibly red.
As the condition progresses, ear pain (otalgia) becomes more prominent. It gradually develops and is initially mild and then becomes more severe if there is no medical intervention. The ear feels full and blocked and there is often associated muffling of sound. Moderate amounts of pus may be evident as thick, foul smelling ear discharge (smelly ear).
In advanced cases, the signs and symptoms are intense. There may be significant hearing loss and severe pain in the affected ear. The pinna of the ear becomes red and swollen. Pain may extend to the jaw, face, neck or head. Swollen neck lymph nodes and fever are often present at this stage.