Otitis Externa

Description

Inflammation of the external auditory canal:

• Acute diffuse otitis externa (AOE) (<6 weeks): most common form; infectious etiology most commonly bacterial (Pseudomonas aeruginosa and Staphylococcus aureus); less commonly fungal (Aspergillus and Candida)
• Chronic otitis externa (>3 months): commonly due to inadequately treated acute otitis externa, persistent allergies, or chronic skin conditions
• Eczematous otitis externa: may accompany typical atopic eczema or other primary skin conditions
• Malignant (necrotizing) otitis externa: an infection that extends into the deeper tissues adjacent to the canal; may include osteomyelitis of the mastoid or temporal bone; a medical emergency requiring urgent referral; can be life-threatening; rare, especially in children (1)
• Synonym: swimmer’s ear

Epidemiology

Incidence

• Annual incidence of ~1% (2)
• Higher in the summer months and in warm, wet climates
• Can affect all age groups but has a peak incidence in 7- to 12-year-olds (3)

Prevalence
Lifetime prevalence of 10% (2)

Etiology and Pathophysiology

• Factors associated with pathogenesis:
  • Skin, cerumen, and surrounding structures provide protection for the integrity of external auditory canal.
  • Cerumen, being a hydrophobic and sticky substance, provides a physical barrier against many foreign particles. Normal cerumen production also creates an environment that is slightly acidic and not favorable for most pathogens.
  • Disruption of the protective skin-cerumen barrier, followed by the subsequent inflammation, swelling, and obstruction of the canal, and impaired cerumen production, are all factors in the development of acute otitis externa.
• AOE, infectious etiology (3):
  • Bacterial infection (>90%): P. aeruginosa (22–62%), Staphylococcus aureus (11–34%); polymicrobial infection is common.
  • Fungal infection (<10%, more commonly associated with chronic otitis externa): Aspergillus (60–90%), Candida species (10–40%)
• Chronic otitis externa etiology: often occurs due to inadequately treated acute otitis externa, persistent allergies, or chronic skin conditions (2)
• Eczematous otitis externa (associated with primary skin disorder) etiology:
  • Eczema, seborrhea, psoriasis
  • Contact dermatitis
  • Purulent otitis media
  • Sensitivity to topical medications
• Malignant (necrotizing) otitis externa etiology (1):
  • Invasive bacterial infection: Pseudomonas, increasing incidence of methicillin-resistant Staphylococcus aureus (MRSA)
  • Associated with patients with diabetes or immunosuppression

Risk Factors

• Acute and chronic otitis externa
  • Water exposure—typically swimming in fresh water
  • Hot, humid weather; sweating
  • Trauma to the external canal—cleaning, scratching, use of instruments
  • Foreign body
  • Use of external devices—hearing aids, ear plugs
  • Anatomic abnormalities—narrow canal, exostoses
  • Dermatologic conditions—eczema, seborrhea, psoriasis
  • Cerumen buildup
  • Excessive hair in canal
  • Previous ear surgery
  • Previous local radiotherapy
• Eczematous: primary skin disorder
• Necrotizing otitis externa in adults
  • Advanced age
  • Diabetes mellitus
  • Immunosuppression (e.g., AIDS, malignancy)

General Prevention

• Avoid prolonged exposure to moisture.
• Use a hair dryer on a low setting to dry the canal.
• Use a head-tilt maneuver to remove excess water.
• Treat predisposing skin conditions.
• Eliminate self-inflicted trauma to canal with cotton swabs and other foreign objects.
• Treat underlying systemic conditions.
• Ear plugs when swimming.