otitis externa

Last edited 04/2021 and last reviewed 07/2021

Otitis externa is a diffuse inflammation of the skin lining the external auditory meatus.

• the external auditory meatus (outer ear canal) is the external part of the ear that lies between the surrounding environment and the middle ear. The outer ear canal is about 2cm long tube, lined by normal skin, ending blindly at the ear drum
• otitis externa is one of the most common pathologies in the ear, and also, one which can be most difficult to treat
• "Mediterranean ear" describes otitis externa which arises as a result of holidaying in hot climates where the patient tends to sweat and bathe more frequently.
  • commonly swimmers are more susceptible; hence the term “swimmer’s ear”(1)
• common condition with an annual incidence of 1% that affects 10% of the population during their lifetime (2)
• the vast majority of cases (98%) the cause is bacterial
  • most common pathogens are Pseudomonas aeruginosa andStaphylococcus aureus
• clinical features include (2)
  • severe otalgia
  • has a impact on quality of life e.g. sleep disturbance, impairment of ability to work or undertake exercise

Note (2,3):

• acute uncomplicated otitis externa can be managed effectively with topical treatments, for up to 14 days if required
• clues for malignant otitis externa include fever, disproportionate pain, or a poor response to first line treatment, particularly in people with diabetes or immunocompromise
  • lavage of the ear canal for cerumen impaction in elderly or diabetic patients, however, has been implicated as a contributing factor in malignant otitis
    externa (3)
  • P aeruginosa is isolated from exudate in the ear canal in more than 90% of cases
  • initial clinical features are those of the initiating acute otitis externa, but untreated disease develops into a skull base osteomyelitis that can invade soft tissue, the middle ear, inner ear, or brain
    • facial nerve paralysis may be an early sign, with the glossopharyngeal and spinal accessory nerves less frequently involved
  • if you suspect malignant otitis externa arrange an urgent (same day) ear, nose, and throat (ENT) review
    • typically a computed tomography imaging scan is required to confirm the diagnosis
• consider cholesteatoma in patients with recurrent discharge
• acute otitis externa can mimic the appearance of acute otitis media (AOM) because of erythema involving the tympanic membrane (3)

Reference:

1. Sander R. Otitis Externa: A Practical Guide to Treatment and Prevention.Am Fam Physician 2001;63:927-36,941-2.
2. Barry V et al. 10-Minute Consultation - Otitis externa. BMJ2021;372:n714http://dx.doi.org/10.1136/bmj.n714
3. Rosenfeld RM, Schwartz SR, Cannon CR, etal. Clinical practice guideline: acute otitis externa.Otolaryngol Head Neck Surg2014;150(Suppl):S1-24.doi: 10.1177/0194599813517083 pmid: 24491310