Introduction

Acute otitis externa (AOE) is an infection of the external ear canal. It is a common presentation in general practice. It is occasionally known as “swimmer’s ear” due to the increased risk in swimming and other water sports, and sometimes “tropical ear” due to its association with humid climates.

It usually presents with ear pain and discharge. There are a wide range of causative organisms, and it is typically a multi-microbial  disorder – with many microbial species involved simultaneously.

Treatment typically involves topical antibiotics, and the majority of cases resolve within a few days.

More rarely, otitis externa is due to inflammation without infection. Typically these cases are chronic. Fungal causes can also cause a chronic illness which is very difficult to treat.

Epidemiology

  • A very common problem presenting to GP practice – accounts for about 1% of all presentations to a GP surgery!
  • 10% of the population will experience an episode in their lifetime
  • 3% of cases will require specialist referral

Aetiology

  • Water penetration of the ear
    • Frequent swimming or other water sports
  • Humidity – more common in tropical locations
  • Trauma to external ear canal
  • Use of cotton wool buds for cleaning the ear
    • This reduces the amount of wax in the canal, which reduces the body’s natural defences
    • It may also cause micro trauma, predisposing to infection
  • Use of hearing aids
  • Ear canal foreign body
  • Presence of external auditory exotosis
    • These are bony growths in the ear canal that appear, on otoscope, like small , rounded “mounds” arising from the wall of the external ear canal.
    • Common in surfers and other individuals who spend a long time in cold water
    • In severe cases, can completely obscure the TM
    • Wax and other debris becomes lodged behind them and leads to frequent and recurrent acute otitis externa
    • If severe, with recurrent infections, they should be surgically removed
    • Less severe cases can be left in situ
    • It is thought that the contact of cold water with the external auditory canal stimulates osteoblast activity – causing the lumps to grown – possibly as a mechanism to protect the TM from the cold

Pathology

Size and shape of the ear canal varies widely between individuals. Some patients are naturally predisposed due to the shape of their canal. The outer 1/3 is made of cartilage, whilst the inner 2/3rds is bony.

The ear canal is naturally self cleaning. The skin of the canal slowly migrates from the TM, along to canal and towards the external auditory meatus. This helps to keep the canal free of debris. Ear wax also helps, by forming an slightly acidic coating, which is toxic to pathogens. It also prevents water from reaching the skin surface. The outer part of the canal is protected by hairs which keep debris out.

Usually multiple organisms are involved. It is thought that water exposure alter the usual microbial balance found in the external ear canal. 90% of cases are bacterial and 10% are fungal.

Common causative organisms include:

  • Pseudomonas
  • Escherichia coli
  • Staphylococci
  • Enterobacter
  • Candida

Chronic otitis media is more likely if there is underlying diabetes or immunosuppression and is typically due to a fungal organism (e.g. candida). Symptoms are typically the same as acute otitis media, and itch and discharge are common. On examination, black dots (fungal spores) may be visible in the external ear canal.

Presentation

  • Ear pain
  • Itching sensation in external ear canal
  • Purulent discharge from external auditory meatus
  • Pre-auricular (in front of the ear) lymphadenopathy
  • Signs of more severe infection include:
    • Hearing loss
    • Discharge
    • Additional regional lymphadenopathy
    • Cellulitis around the ear
    • Fever
  • Necrotising (malignant) otits externa
    • A potentially life-threatening complication
    • Occurs when the infection has spread to the mastoid and temporal bones
    • Severe pain – out of proportion to other clinical signs
    • Typically occurs in older patients who are otherwise immunocompromised
    • Facial nerve palsy may also be a sign

Investigations

Consider investigations in recurrent infection, or cases not responding to first line therapy. Identifying the organism rarely changes management. False positives for fungi are common in partially treated cases.

  • Swab of discharge for MC+S

Differentials Diagnosis

  • Acute Otitis Media
  • Foreign body
  • Impacted wax
  • Cholasteatoma

Management

  • Aural Toilet
    • A method of cleaning the external canal. Usually performed by the medical practitioner at the time of diagnosis – for example, micro-suction, dry swabbing or gentle ear syringing
      • Be aware that ear syringing carries a risk of perforation of the tympanic membrane (TM), and is also contraindicated if TM perforation is already present. In some guidelines it is no longer recommended
    • Aural toilet lowers pH of the external canal – which helps increase the effectiveness of amino glycoside drops
  • Ear wicking
    • A device inserted into the ear, impregnated with antibiotics and steroids
    • Usually requires ENT referral for placement
    • Should be changed every 2-3 days
  • Acetic acid
    • As effective as antibiotics in mild cases
    • Less effective in severe cases
    • Generally, antibiotics are preferred
  • Topical antibiotics are the mainstay of treatment e.g.:
    • “Sofradex” ear drops – a combination preparation with framycetin (an aminoglycoside containing neomycin – good Gram-positive and Gram-negative cover), gramicidin (an antibiotic compound containing multiple antimicrobial agents – mainly gram negative cover) and dexamthasone (a corticosteroid). Care should be taken if there is a risk of TM rupture, because aminoglycosides can disrupt healing of the TM and thus are contraindicated
    • Ciprofloxacin ear drops – first line is TM rupture suspected or proven
    • Prolonged use of antibiotics can cause a local contact sensitivity – which can mimic ongoing symptoms of otitis externa (itchy, painful, red looking canal on otoscopy)
    • Drops should be used for at least a week
    • Most cases resolve within 6 days
  • Analgesia
    • Paracetamol or NSAIDs
    • NSAID’s may be slightly more effective
  • Oral antibiotics
    • Can be used in cases with complications (such as TM rupture)
    • Indications include:
      • Systemic features
      • Pre-aurcilar lymphadenoapthy
      • Spreading infection – e.g. cellulitis of the ear
    • Usual antibiotic of choice is flucloxacillin (or erythromycin in penicillin allergy) – the most common causative organism in these case is staph. aureus. 
    • Several studies have shown that oral antibiotics are generally over-prescribed
  • Indications for referral
    • Systemic symptoms – need urgent referral for possible IV antibiotics
    • Chronic cases
      • Consider use of topical clotrimazole drops if fungal infection is suspected
  • Necrotising otits externa
    • 90% of cases due to pseudomonas
    • Usually responds to oral quinolone – but may require up to 8 weeks of treatment
  • Avoid swimming until symptoms have settled
  • Avoid plugging the ear with cotton wool – some patients like to try this to prevent unsightly (and smelly) discharge, but can worsen the infection

Complications

  • Temporary hearing loss
  • Chronic otitis externa
  • Cellulitis
  • Necrotising otitis externa
    • May cause secondary sepsis

Prevention

  • Avoid water getting into the external canal. Measure may include:
    • Use of ear plugs and / or cotton wool coated with vaseline when swimming
    • Keeping head above water wherever possible
    • Avoid swimming in dirty or polluted water sources
  • Dry ears well after swimming and bathing
    • Recommended method is a tissue spear. This involves taking a tissue and twisting it into a tip with your fingers.
  • Avoid putting anything into the ear canal – finger, cotton buds or other “cleaning” agents. The ear is remarkable good at cleaning itself!

References

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