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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Classic finding: ear pain worsened by tragal pressure or pinna movement with an edematous ear canal
- Most common pathogens: Pseudomonas aeruginosa and Staphylococcus aureus
- First-line treatment is topical antibiotic drops, often with a steroid; oral antibiotics are usually unnecessary
- Avoid aminoglycoside-containing drops if tympanic membrane perforation or tube is possible; use fluoroquinolone drops instead
- Severe otalgia in an older diabetic or immunocompromised patient = malignant otitis externa until proven otherwise
Overview
Otitis externa is inflammation of the external auditory canal, usually infectious and precipitated by moisture, trauma from cotton swabs, hearing aids, eczema, or obstruction. The key anatomical distinction from AOM is that the disease is in the canal rather than the middle ear. Pain with tragal pressure or pinna traction is a high-yield differentiator. Malignant otitis externa, also called necrotizing otitis externa, is an invasive skull-base osteomyelitis usually due to Pseudomonas in older adults with diabetes or immunocompromise.
Epidemiology
Acute otitis externa is common in warm, humid environments and among swimmers. It affects children and adults, with increased risk after local trauma or water exposure. Chronic otitis externa may reflect dermatologic disease such as eczema, psoriasis, contact dermatitis, or chronic fungal infection. Necrotizing otitis externa is uncommon but high-risk, especially in patients with diabetes, HIV, chemotherapy, or other immunosuppression.
Clinical Features
Symptoms
Severe otalgia, often disproportionate to exam findings
Pruritus, ear fullness, or muffled hearing from canal edema
Purulent otorrhea with canal debris
Pain after swimming, earbud use, hearing aid irritation, or cotton-swab trauma
Deep nocturnal otalgia in an older diabetic or immunocompromised patient
Facial weakness, dysphagia, hoarseness, or diplopia suggests skull-base spread
Signs
Pain with tragal pressure or pinna traction — hallmark finding
Edematous, erythematous external canal with debris; tympanic membrane may be hard to visualize
Normal middle-ear landmarks if TM visible; helps distinguish from AOM
Granulation tissue at the bony-cartilaginous canal junction suggests necrotizing otitis externa
Cranial neuropathies VII, IX, X, XI, or XII are late red flags
Investigations
First-line
Clinical diagnosis by otoscopyMost cases need no labs or imaging. Assess canal patency, TM integrity, and severity of edema
Differentiate from AOMAOM has bulging TM and middle-ear effusion; otitis externa has canal edema and tragal/pinna tenderness
Second-line
Culture canal drainageSevere, recurrent, immunocompromised, chronic, or treatment-resistant cases
Glucose/HbA1c if risk factorsScreen for diabetes when necrotizing otitis externa is suspected or infections are unusually severe
Specialist
CT temporal bone or MRI skull baseIf necrotizing otitis externa suspected. CT shows bony erosion; MRI better defines soft tissue and intracranial spread
ESR/CRPOften elevated in necrotizing otitis externa and useful for monitoring response to therapy
ENT referralSevere canal obstruction needing debridement/ear wick, suspected necrotizing disease, cranial neuropathy, or failure of therapy
1
Uncomplicated acute otitis externa
- Topical therapy first-line: ciprofloxacin, ofloxacin, or polymyxin B/neomycin/hydrocortisone if TM intact
- Prefer fluoroquinolone drops if TM perforation, tympanostomy tube, or uncertain TM integrity
- Add topical steroid combination when inflammation and edema are prominent
- Analgesia with NSAIDs or acetaminophen; severe pain may require short-course oral analgesia
2
Improve delivery of drops
- Aural toilet/debridement by trained clinician if debris blocks penetration
- Ear wick if canal is markedly edematous; apply drops to wick and reassess within 24-48 h
- Keep ear dry; avoid swimming and cotton swabs during treatment
3
When systemic antibiotics are indicated
- Do NOT use oral antibiotics for uncomplicated diffuse otitis externa
- Use systemic antibiotics if extension beyond ear canal, cellulitis, diabetes/immunocompromise, or suspected necrotizing otitis externa
4
Necrotizing otitis externa
- Urgent ENT/infectious disease involvement
- Antipseudomonal systemic therapy such as ciprofloxacin or IV cefepime/ceftazidime/piperacillin-tazobactam depending on severity and resistance risk
- Serial ESR/CRP and imaging/clinical monitoring; prolonged treatment is usually required
Complications
- Canal stenosis: Chronic inflammation may narrow the external auditory canal
- Periauricular cellulitis: Infection extends beyond the canal
- Necrotizing otitis externa: Skull-base osteomyelitis with cranial neuropathies, usually Pseudomonas
- Conductive hearing loss: From canal edema or debris
- Medication ototoxicity: Aminoglycoside drops can harm the inner ear if the TM is not intact
USMLE Step 2 CK Exam Tips
- 1Tragal tenderness/pinna pain = otitis externa; bulging TM = acute otitis media
- 2Topical drops, not oral antibiotics, are first-line for uncomplicated otitis externa
- 3Use fluoroquinolone drops when TM perforation cannot be excluded
- 4Canal too swollen for drops = place an ear wick
- 5Diabetic + severe ear pain + granulation tissue = malignant otitis externa — image skull base and give antipseudomonal therapy
- 6Cotton swabs and swimming are classic precipitating factors
- 7Cranial nerve palsy in otitis externa is a red flag for skull-base osteomyelitis
practicetest your knowledge on otitis externaApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — ent and beyond.
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