Acute inflammation of the external auditory canal, usually bacterial, often associated with water exposure.
Also known as: otitis externa, swimmer's ear, AOE, external ear infection, necrotizing otitis externa, malignant otitis externa
Overview
Diffuse inflammation of the external auditory canal (EAC), with or without involvement of the auricle or tympanic membrane. Acute (≤6 weeks) is most often bacterial; chronic (>3 months) may be fungal, allergic, or dermatologic.
Epidemiology
Annual incidence ~1% in the US; peak ages 7-12. Increased in summer, in swimmers, and in humid climates. Necrotizing (malignant) otitis externa occurs almost exclusively in diabetics and immunocompromised patients.
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Question 1EENTMedium
A 70-year-old female with diabetes has a 3-week history of severe constant right ear pain, purulent drainage, and granulation tissue at the floor of the external auditory canal. She now has right facial nerve palsy. CT temporal bone shows cortical erosion at the skull base. Which of the following organisms is most likely responsible?
APseudomonas aeruginosa
BStreptococcus pneumoniae
CAspergillus fumigatus
DStaphylococcus aureus
Reveal answer & full explanation
Correct answer: A — Pseudomonas aeruginosa
APseudomonas aeruginosa✓
BStreptococcus pneumoniae
CAspergillus fumigatus
DStaphylococcus aureus
Why Pseudomonas aeruginosa is correct
Malignant (necrotizing) external otitis is caused by Pseudomonas aeruginosa in over 95% of diabetic patients
Hallmarks: severe constant otalgia, purulent otorrhea, and granulation tissue at the bony-cartilaginous junction of the external auditory canal floor — the pathognomonic location
Cranial nerve VII is the most commonly involved cranial nerve, consistent with this patient's facial nerve palsy
Why the others are wrong
Streptococcus pneumoniae — is a common cause of otitis media and sinusitis, not malignant external otitis (confused-with otitis media)
Aspergillus fumigatus — is a rare cause seen primarily in immunocompromised non-diabetic patients, not the predominant organism here (zebra over horse)
Staphylococcus aureus — can cause external otitis but is not the organism in over 95% of MEO cases in diabetics (anchoring on common skin flora)
Additional high-yield points
Diagnosis supported by CT temporal bone (bony erosion), MRI (soft tissue extent), and gallium-67 or PET-CT (to monitor response)
Treatment: IV ciprofloxacin for Pseudomonas coverage and bone penetration; alternatives piperacillin-tazobactam, cefepime, or meropenem
Duration: minimum 6-8 weeks, guided by gallium scan and clinical response
Surgical debridement is conservative; hyperbaric oxygen is an adjunct for refractory cases
Question 2EENTMedium
A 19-year-old competitive swimmer presents with 2 days of right ear pain and fullness. He denies fever, recent upper respiratory infection, or prior ear surgery. On exam, manipulation of the tragus and traction on the pinna reproduce severe pain. The external auditory canal is erythematous, edematous, and filled with debris; the tympanic membrane appears intact where visible. He is diagnosed with acute otitis externa, and a culture grows Pseudomonas aeruginosa. Which of the following best explains the findings?
AReactivation of latent varicella-zoster virus in the geniculate ganglion of CN VII
BKeratin debris trapped in a retraction pocket gradually eroding adjacent temporal bone
CLoss of the protective cerumen layer allowing bacterial overgrowth in a moist canal
DEustachian tube dysfunction causing middle-ear fluid behind the tympanic membrane
Reveal answer & full explanation
Correct answer: C — Loss of the protective cerumen layer allowing bacterial overgrowth in a moist canal
AReactivation of latent varicella-zoster virus in the geniculate ganglion of CN VII
BKeratin debris trapped in a retraction pocket gradually eroding adjacent temporal bone
CLoss of the protective cerumen layer allowing bacterial overgrowth in a moist canal✓
DEustachian tube dysfunction causing middle-ear fluid behind the tympanic membrane
Why Loss of the protective cerumen layer allowing bacterial overgrowth in a moist canal is correct
Cerumen is acidic and lipid-rich, creating a hydrophobic, low-pH barrier that inhibits bacterial growth in the external auditory canal.
Repeated water exposure (swimming) washes away cerumen and raises canal pH and humidity; the warm, moist, denuded epithelium becomes an ideal medium for overgrowth of Pseudomonas aeruginosa (~50%) and Staphylococcus aureus (~20%).
Pain with tragal pressure and pinna traction plus a diffusely edematous, debris-filled canal with an intact TM is the classic picture of acute otitis externa, an infection of the canal skin itself.
Why the others are wrong
Eustachian tube dysfunction causing middle-ear fluid behind the tympanic membrane is the mechanism of acute otitis media/effusion; it produces a bulging or dull TM and pain on deep insertion, not the canal edema and tragal tenderness seen here.
Keratin debris trapped in a retraction pocket gradually eroding adjacent temporal bone describes cholesteatoma, which causes painless foul otorrhea and conductive hearing loss, not an acutely painful swimmer with an intact TM.
Reactivation of latent varicella-zoster virus in the geniculate ganglion of CN VII is herpes zoster oticus (Ramsay Hunt), which presents with auricular/canal vesicles, facial nerve palsy, and vertigo, none of which are present here.
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Diabetes mellitus, immunosuppression — risk for necrotizing otitis externa
Cerumen removal that strips protective lipid layer
Pathophysiology
Loss of cerumen and disruption of the canal epithelium allow bacterial overgrowth in a warm, moist environment. Pseudomonas aeruginosa (~50%) and Staphylococcus aureus (~20%) are most common. Fungal etiologies (Aspergillus niger, Candida albicans) cause otomycosis, often after prolonged topical antibiotic use.
Clinical presentation
Symptoms
Ear pain, often severe and out of proportion to visible findings
Pruritus (especially fungal)
Sensation of fullness or hearing loss from canal swelling
Otorrhea — purulent, scant, or watery
Signs / physical exam
Tenderness on tragal pressure or pinna traction — classic distinguishing sign from AOM
Erythematous, edematous canal with debris or discharge
TM often obscured; if visible, usually normal
Periauricular lymphadenopathy
Conductive hearing loss if canal occluded
Classic findings
Pain with tragal/pinna manipulation plus erythematous, debris-filled canal.
Differential diagnosis
Acute otitis media with perforation — Otorrhea preceded by ear pain that resolved with TM rupture; canal usually less swollen than in AOE; bulging or perforated TM
Otomycosis — Pruritus > pain, white/black fungal debris ('wet newspaper'), often follows topical antibiotic course; treat with acidifying drops or clotrimazole
Necrotizing (malignant) otitis externa — Diabetic or immunocompromised; deep boring pain disproportionate to exam, granulation tissue at bony-cartilaginous junction, cranial nerve palsies; CT/MRI, IV antipseudomonal therapy
Furunculosis — Localized hair-follicle abscess in cartilaginous canal; treat with incision/drainage and anti-staph antibiotics
Contact dermatitis — Pruritus, eczematous canal, history of neomycin or other allergen; treat by removing offending agent and topical steroid
Herpes zoster oticus (Ramsay Hunt) — Vesicles on auricle/canal, facial nerve palsy, vertigo; treat with antivirals and corticosteroids
AAO-HNS 2014: rapid onset (≤48 h) within last 3 weeks PLUS symptoms of ear canal inflammation (otalgia, itching, fullness) PLUS signs of canal inflammation (tenderness of tragus/pinna OR diffuse canal edema/erythema).
Labs
Clinical diagnosis; cultures rarely needed in uncomplicated AOE
Culture if treatment failure, recurrent, immunocompromised, or suspected necrotizing OE
ESR, CRP, glucose/A1c, and CT temporal bone if necrotizing OE suspected
Imaging
Not routinely needed for uncomplicated AOE
CT temporal bone with contrast or technetium-99m bone scan if malignant OE suspected (bony erosion, skull base osteomyelitis)
MRI with gadolinium to evaluate intracranial extension
Diagnostic algorithm
Feature
Otitis Externa
Otitis Media
Pain on tragal pressure
Yes (hallmark)
No
Pain on pinna traction
Yes
No
Canal appearance
Erythematous, swollen, debris
Normal
TM appearance
Often obscured; normal if seen
Bulging, opaque, erythematous
Fever
Usually absent
Often present
Hearing loss
Conductive from canal occlusion
Conductive from effusion
Treatment
Topical otic drops
Oral antibiotic (amoxicillin)
Bedside differentiation of otitis externa from acute otitis media.
Treatment
First-line
Topical otic antibiotic — ofloxacin 0.3%, ciprofloxacin/dexamethasone, or neomycin/polymyxin B/hydrocortisone × 7-10 days
Use fluoroquinolone-containing drops (ofloxacin or ciprofloxacin) if TM perforation or tympanostomy tubes present — neomycin and aminoglycosides are ototoxic
Aural toilet (gentle suction/curettage under direct vision) to remove debris and allow drop penetration
Wick placement (Pope or ribbon gauze) if canal severely edematous; remove in 48-72 h
Oral analgesia — acetaminophen or NSAIDs; opioids for severe pain
Dry ear precautions — no swimming, earplug for bathing × 7-10 days
Second-line / adjunct
Otomycosis: cleansing followed by topical clotrimazole 1% solution, gentian violet, or acidifying drops (acetic acid 2%)
Furuncle: warm compresses, incision/drainage if fluctuant, oral anti-staph (dicloxacillin, cephalexin, or doxycycline)
Systemic antibiotics rarely needed; add if cellulitis extends beyond canal or in immunocompromised
Necrotizing otitis externa: hospitalization, IV antipseudomonal (ciprofloxacin, piperacillin-tazobactam, or cefepime) × 6-8 weeks plus ENT consultation
Prevention: acetic acid + isopropyl alcohol drops after swimming
Complications
Cellulitis of the auricle or face
Chronic otitis externa with canal stenosis
Tympanic membrane perforation
Necrotizing (malignant) otitis externa with skull base osteomyelitis, cranial neuropathies (especially CN VII), meningitis
Permanent hearing loss in rare advanced cases
PANCE pearls
Pain with pulling on the pinna or pressing the tragus → otitis externa; pain only with deep insertion → otitis media.
Avoid aminoglycoside-containing drops (neomycin) if TM perforation is suspected — risk of ototoxicity.
In a diabetic patient with severe otalgia, deep pain, granulation tissue at the cartilage-bone junction, and facial nerve weakness — suspect necrotizing otitis externa. Pseudomonas is the dominant pathogen.
Black or white fluffy debris ('wet newspaper') in canal = fungal — antibacterial drops will fail or worsen it.
Acidifying drops (2% acetic acid) prevent recurrent swimmer's ear and treat early mild cases.
References
AAO-HNS 2014 — Rosenfeld RM et al. Clinical Practice Guideline: Acute Otitis Externa. Otolaryngol Head Neck Surg 2014;150(1S):S1-S24
AAFP — Schaefer P, Baugh RF. Acute otitis externa: an update. Am Fam Physician 2012;86(11):1055-1061
IDSA — Hollis S, Evans K. Management of malignant (necrotising) otitis externa. J Laryngol Otol 2011
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