Otitis externa: causes and clinical features
Otitis externa is inflammation of the skin lining the external auditory canal (the tube between the outer ear and the eardrum), usually from infection.
Remember
Pain on pulling the pinna (the visible outer ear) or pressing the tragus (the small flap in front of the canal opening) places the problem in the ear canal: think acute otitis externa, typically after water exposure.
Memory aid
Think of earwax as the canal's raincoat
Picture cerumen as a raincoat for the canal: strip it away with water and trauma, and the skin underneath is open to infection.
The ear canal is normally protected by cerumen, the earwax. It is acidic and repels water, so microbes are discouraged from growing there. Trapped water, swimming, cotton buds and other objects can strip that protection away or scratch the thin canal skin. Foreign bodies are another risk factor.
Once the barrier is stripped away, microbes can take hold. Most cases are infective: about 90% of these are bacterial, commonly Pseudomonas aeruginosa or Staphylococcus aureus, and about 10% fungal.
Patients typically have an itchy, painful ear with discharge. The canal looks red and swollen, with moist debris inside. In acute otitis externa the hallmark sign is pain when the pinna is pulled or the tragus is pressed, because both movements disturb the inflamed lining of the canal. Middle ear disease lies behind the eardrum, out of reach when the outer ear is tugged.
The name gives the site: externa is the canal outside the eardrum, whereas media is the middle ear, the air-filled space behind it.
Hearing can be mildly reduced. A narrowed canal lets less sound through to the eardrum. This is conductive hearing loss, meaning a problem with sound passing through the outer or middle ear, not a problem of the inner ear or hearing nerve.
Key facts
- Site
- the skin lining the ear canal, which runs between the outer ear and the eardrum.
- Triggers
- trapped water, swimming, cotton buds and foreign bodies.
- Organisms
- about 90% bacterial, commonly Pseudomonas aeruginosa or Staphylococcus aureus, and about 10% fungal.
- Hallmark sign (acute otitis externa)
- marked pain on moving the pinna or pressing the tragus.
- Other features
- itch, discharge, and a red, swollen canal with moist debris, so the eardrum may be hard to see.
- Hearing
- a mild conductive hearing loss can follow if swelling or debris narrows the canal.
- Bedside clue
- pain when the pinna is pulled or the tragus pressed points to the canal (externa), while a bulging eardrum points to the middle ear (media).
Exam traps
- Pain with a bulging tympanic membrane (the eardrum) points to acute otitis media, an infection behind the drum in the middle ear, not to otitis externa, although the canal condition can also be very painful.
- Acute mastoiditis (a bacterial infection of the air cells in the mastoid bone behind the ear) causes tenderness, redness and swelling behind the ear rather than primary inflammation of the canal skin, and the condition usually arises after acute otitis media.
- Ramsay Hunt syndrome is shingles of the facial nerve, from reactivation of the varicella zoster virus. It brings a blistering (vesicular) rash in the ear, and facial weakness and hearing loss are often present, so without blisters or a facial droop it does not explain the picture.
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