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Summary Table

Feature	Details
Risk Factors	Swimming ("swimmer's ear"), humid climates, hearing aid use, cotton swab trauma, eczema or psoriasis of the ear canal, immunocompromised state (diabetes mellitus for malignant otitis externa)
Etiology	Pseudomonas aeruginosa (most common), Staphylococcus aureus; fungal causes (Aspergillus, Candida) in otomycosis
Patient Presentation	Ear pain (otalgia) worsened by chewing or jaw movement, pruritus, aural fullness, possible otorrhea
Classic Physical Exam	Pain on tragal pressure or pinna traction, edematous and erythematous ear canal, debris or discharge in the canal, intact tympanic membrane
Key Diagnostic Results	Clinical diagnosis; culture of discharge only if refractory; CT temporal bone if malignant otitis externa is suspected
Management	Topical antibiotic drops (fluoroquinolone preferred), aural toilet, wick placement if canal is severely swollen; systemic antipseudomonal antibiotics for malignant otitis externa
Keywords	"Swimmer's ear," "pain with tragal pressure," "pain with pinna traction," "ear canal edema," "granulation tissue at the bony-cartilaginous junction" (malignant OE)

1. Pathophysiology

The external auditory canal is lined by skin that produces cerumen, which serves as a protective acidic barrier (pH ~5) against bacterial and fungal colonization. When this barrier is disrupted, whether by excessive moisture, mechanical trauma, or dermatologic conditions, the canal becomes vulnerable to infection.

Water exposure is the single most important predisposing factor. Prolonged moisture raises the canal pH and causes maceration of the epithelial lining, creating a warm, alkaline environment ideal for bacterial proliferation. This is why the condition is strongly associated with swimmers and humid climates.

Pseudomonas aeruginosa thrives in moist environments and accounts for the majority of cases. Once the organism colonizes the damaged epithelium, it triggers an inflammatory response that produces the hallmark findings: canal edema, erythema, and purulent discharge. The swelling of the canal skin explains why patients report aural fullness and conductive hearing loss when the lumen narrows significantly.

Pain with tragal pressure and pinna traction occurs because the cartilaginous portion of the external canal is directly continuous with these structures. Any manipulation transmits force to the inflamed canal wall, distinguishing this condition from otitis media, where these maneuvers are painless.

In immunocompromised patients, particularly those with poorly controlled diabetes mellitus, the infection can extend beyond the canal soft tissue into the temporal bone. This is malignant (necrotizing) otitis externa, a life-threatening osteomyelitis of the skull base. The pathologic hallmark is granulation tissue at the bony-cartilaginous junction of the ear canal. Cranial nerve involvement, beginning with cranial nerve VII (facial nerve), signals advanced disease. If the infection spreads further along the skull base, cranial nerves IX, X, and XI can be affected.

2. Classification and Clinical Manifestations

Type	Population	Key Features	Severity
Acute diffuse otitis externa	Swimmers, humid climate exposure	Otalgia, pruritus, canal edema, otorrhea, pain with tragal pressure; intact tympanic membrane	Mild to moderate
Chronic otitis externa	Patients with allergic or dermatologic conditions (eczema, psoriasis)	Persistent pruritus more than pain, dry flaky canal skin, thickened canal from chronic inflammation	Low grade, recurrent
Otomycosis	Prolonged topical antibiotic use, immunosuppressed, tropical climates	Fluffy white or black debris in canal (Aspergillus niger produces dark spores), intense pruritus, less pain than bacterial OE	Mild
Malignant (necrotizing) otitis externa	Elderly diabetics, immunocompromised (HIV, chemotherapy)	Severe deep-seated otalgia disproportionate to exam, granulation tissue at bony-cartilaginous junction, cranial neuropathies (CN VII first), possibly fatal	Life-threatening

3. Diagnostic Workup

Test	Role	Key Findings
Clinical examination	Best initial and usually only test needed for uncomplicated OE	Tragal tenderness, pinna traction pain, canal edema, otorrhea, intact TM
Culture of ear discharge	Reserved for refractory or recurrent cases	Identifies organism and sensitivities; important when empiric therapy fails
CT of the temporal bone	Best initial imaging for suspected malignant OE	Bony erosion of the external auditory canal and skull base
Technetium-99m bone scan	Most sensitive test for malignant OE	Detects osteoblastic activity early; useful for initial diagnosis
Gallium-67 scan	Monitor treatment response in malignant OE	Normalizes with successful treatment (unlike Tc-99m, which stays positive long after infection resolves)
ESR / CRP	Adjunctive markers in malignant OE	Elevated; useful for tracking treatment response

Uncomplicated otitis externa is a clinical diagnosis. The combination of otalgia worsened by tragal pressure or pinna traction, a swollen erythematous canal, and an intact tympanic membrane is sufficient. No labs or imaging are needed in the straightforward case.

When a patient fails to respond to appropriate topical therapy after 2 to 3 weeks, obtain a culture of the ear discharge to guide targeted treatment. This is particularly important to identify fungal infections (otomycosis) or resistant organisms.

If the clinical picture suggests malignant otitis externa, the urgency of the workup changes entirely. The combination of an elderly diabetic patient with severe ear pain, granulation tissue in the canal, and cranial nerve deficits should prompt CT of the temporal bone to assess for bony erosion. A Tc-99m bone scan is the most sensitive study to detect early osteomyelitis when CT findings are equivocal. Once treatment begins, gallium-67 scanning is the preferred modality to monitor response, because it reflects active infection rather than bone remodeling.

4. Management and Treatment

Scenario	Treatment	Details
Mild uncomplicated OE	Topical acidifying drops	Acetic acid 2% drops, 3 to 5 drops 3 times daily for 7 days
Moderate uncomplicated OE	Topical fluoroquinolone with or without corticosteroid	Ofloxacin 0.3% or ciprofloxacin 0.2%/dexamethasone 0.1%, 3 to 4 drops twice daily for 7 to 10 days
Severely edematous canal	Ear wick + topical drops	Place a compressed wick into the canal to deliver medication past the obstruction; remove at 2 to 3 days
Otomycosis	Topical antifungal	Clotrimazole 1% solution, applied twice daily for 2 to 3 weeks; thorough aural toilet is essential
Malignant otitis externa	Systemic antipseudomonal antibiotics	IV ciprofloxacin 400 mg every 8 to 12 hours or IV piperacillin-tazobactam; prolonged course of 6 to 8 weeks; surgical debridement if needed

The first step in managing any form of otitis externa is aural toilet, meaning gentle cleaning and removal of debris from the canal under direct visualization. Topical medications cannot penetrate through accumulated discharge and cerumen, so clearing the canal is essential before starting drops.

For uncomplicated cases, topical fluoroquinolone drops (ofloxacin or ciprofloxacin/dexamethasone combination) are the treatment of choice. Fluoroquinolones are preferred because they are effective against Pseudomonas, are non-ototoxic, and can be used safely even if there is uncertainty about tympanic membrane integrity. Aminoglycoside-containing drops (neomycin/polymyxin B/hydrocortisone) are an alternative but carry a risk of ototoxicity if the tympanic membrane is perforated. This distinction is a commonly tested decision point.

When canal edema is severe enough that drops cannot reach the medial canal, a compressed ear wick should be placed. The wick expands with the topical solution and acts as a conduit to deliver medication deeper into the canal. It is typically removed after 2 to 3 days once the swelling has subsided.

Patients should be counseled to keep the ear dry during treatment: no swimming, use of cotton balls with petroleum jelly during showers, and avoidance of cotton swabs.

For malignant otitis externa, topical therapy alone is insufficient. These patients require prolonged systemic antipseudomonal antibiotics, typically IV ciprofloxacin or piperacillin-tazobactam, for a minimum of 6 weeks. Oral ciprofloxacin 750 mg twice daily may be used for step-down therapy in stable patients. Treatment is guided by gallium scan normalization and inflammatory marker trends rather than a fixed calendar duration.

5. Differential Diagnosis and Distractors

Differential	Why It Is Similar	Key Discriminator
Acute otitis media (AOM)	Both cause ear pain and can present with discharge if the TM perforates	AOM has a bulging, erythematous tympanic membrane with middle ear effusion; tragal pressure and pinna traction are not painful in AOM
Contact dermatitis of the ear canal	Pruritus, erythema, and canal skin changes overlap with chronic OE	History of exposure to earrings, hearing aid materials, or new ear drops; more pruritus than pain; vesicular or weeping lesions
Herpes zoster oticus (Ramsay Hunt syndrome)	Severe ear pain with possible facial nerve palsy, similar to malignant OE	Vesicular eruption on the pinna or canal, ipsilateral facial paralysis, sensorineural hearing loss; caused by VZV reactivation in the geniculate ganglion
Referred otalgia (TMJ dysfunction)	Ear pain worsened by jaw movement, mimicking OE	Normal ear canal on examination; pain reproduced by palpation of the temporomandibular joint; no canal edema or discharge
Cholesteatoma with secondary infection	Foul otorrhea and hearing loss can resemble OE	Retraction pocket or pearly white mass behind TM; conductive hearing loss with abnormal TM; CT shows bony erosion in the middle ear, not the canal
Squamous cell carcinoma of the ear canal	Chronic unilateral otorrhea and pain unresponsive to treatment	Tissue mass in the canal, bloody discharge, cranial neuropathies possible; biopsy is diagnostic

6. Traps and High-Yield Pearls

The single most common trap with otitis externa questions involves distinguishing it from acute otitis media. Both conditions cause ear pain and can produce discharge from the ear. The discriminating maneuver is tragal pressure or pinna traction: if this reproduces the pain, the pathology is in the external canal, not the middle ear. A vignette describing a child with ear pain after swimming who has pain when you pull the ear should immediately point you toward otitis externa, even if you are tempted to think about otitis media given the patient's age.

A second high-yield trap involves drop selection when the tympanic membrane status is uncertain. If the vignette does not clearly state the TM is intact, or if perforation cannot be excluded, always choose a fluoroquinolone drop over an aminoglycoside-containing preparation. Neomycin and gentamicin are ototoxic if they reach the middle ear through a perforation. Selecting the wrong drop in this scenario is a favorite wrong-answer trap.

The third major testing concept is the recognition of malignant otitis externa. The classic vignette is an elderly patient with diabetes who presents with severe, unrelenting ear pain disproportionate to examination findings, granulation tissue at the floor of the ear canal, and an elevated ESR. When facial nerve palsy is added to this picture, the diagnosis is essentially confirmed. The tested competency here is recognizing that this is not simply a "bad ear infection" but an invasive osteomyelitis requiring weeks of systemic antibiotics and imaging surveillance.

Finally, remember that otomycosis often appears as a secondary diagnosis: a patient who was already treated for bacterial otitis externa with prolonged antibiotic drops and now returns with intense itching and fluffy or dark debris in the canal. The tested concept is recognizing antibiotic-induced fungal superinfection and switching to a topical antifungal agent.

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