Acute otitis externa (AOE) is defined as diffuse inflammation of the external ear canal, which may also involve the pinna or tympanic membrane.1 AOE is a form of cellulitis that involves the skin and sub dermis of the external auditory canal, with acute inflammation and variable oedema1 . It is most commonly caused by bacterial infection of the external ear canal following swimming.1,6 The most common pathogens isolated from culture are Pseudomonas aeruginosa and/or Staphylococcus aureus. Other pathogens both bacterial and fungal are much less common, though Candida or Aspergillus species are often the alternate pathogens found on culture, particularly after prolonged antibiotic use.6 The diagnosis of AOE requires the presence of rapid onset of symptoms (generally within 48 hours) within the past 3 weeks, coupled with signs of ear canal inflammation1,9 . AOE has a lifetime incidence of 10%.1,3,8 AOE is prevalent worldwide and is known to affect people of all age groups but is found to peak in the 5 - 14 year old age group and decline with increasing age. The incidence of AOE is increased in summer months due to a causal relationship with prolonged water exposure and high humidity9 , hence its colloquial name of “swimmer’s ear”. Otitis externa has acute (<6 weeks), chronic (>3 months), and necrotising (malignant) forms and may present as a single episode or may recur.
The pathophysiology of AOE is attributable to the decreased integrity of the external auditory canal, whose
protective environment is usually hydrophobic, acidic and containing a protective ceruminous layer. Disruption
of this environment therefore exposes the epithelium of the external canal to water and bacterial infection.2
Infection of the external canal epithelium leads to an acute inflammatory reaction causing erythema and
oedema of the canal. Symptomatically this results in otalgia, ottorhea, pruritus and jaw pain. If oedema is
severe, hearing loss may result from occlusion of the canal.2
A number of factors can contribute and predispose certain individuals to a higher risk of infection.1,2,8,9
• Water exposure
• Localised or generalized eczema
• Immunocompromised patients
• Diabetes Mellitus
• Use of hearing aids, plugs or cotton ear buds
• Anatomical obstructions (exostoses or canal stenosis)
• Physiological (decreased ear wax production)
Complications
Malignant (necrotising or skull base osteomyelitis) otitis externa is a serious and potentially fatal complication
of AOE. This complication affects immunocompromised individuals such as those with chemotherapy-induced
aplasia, refractory anaemia, chronic leukaemia, lymphoma, splenectomy, neoplasia and renal transplantation2
.
Pathophysiology in this case reflects spread of the infection through the floor of the external auditory canal to
the base of the skull, with associated formation of granulation tissue. P. aeruginosa is the most common cause
however fungal pathogens can also cause the condition especially in patients with AIDS, in whom Aspergillus
fumigatus is the most common pathogen. These patients have typically failed appropriate topical and/or
systemic antibiotic therapy. On examination the external auditory canal may show presence of granulation
tissue or a polyp on the floor of the canal, as well as exposed bone. Extension into the skull base may result
in cranial neuropathies, with the facial nerve most commonly involved. Carcinoma of the ear canal has a similar
appearance and biopsy is necessary to rule out malignancy.2 All suspected cases of malignant otitis externa
should be discussed with ENT in a timely manner.
Disposition
Due to the generally uncomplicated nature of AOE, disposition of patients is usually discharge from hospital
with close follow up arranged either with a primary care physician at the 48-72h mark or in ENT outpatient
clinic (especially if ear toilet is required). Advice should be given about the prevention of recurrence –
particularly ensuring ears are dry post water sports and consideration of the use of ear plugs. If analgesic
requirements are significant then consultation with ENT registrar for review or admission to hospital may be
required. If systemic illness is present then a consult with ENT Registrar on call would be appropriate. If there
is a concern for any of the alternative diagnosis other than uncomplicated AOE then ENT consult should be
sought in a timely manner.
Consultation
Key stakeholders who reviewed this version:
• Paediatric Emergency SMO, QCH
• Director, Paediatric Otolaryngology Head and Neck Surgery, QCH
• Director, Infectious Diseases, QCH
• AMS Pharmacist, QCH
• Medicines Advisory Committee – endorsed 17/11/2022