Otitis Eksterna

01Pathophysiology

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.

02Classification and Clinical Manifestations

03Diagnostic Workup

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.

04Management and Treatment

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.

05Differential Diagnosis and Distractors

06Traps 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.