Acute Diffuse Otitis Externa

Condition

Often follows water exposure and maceration of the skin — the main mechanism is moisture trapping (swimming, ear muffs, perspiration). Other contributing factors: trauma (ear cleaning); medical conditions (diabetes, psoriasis, immunosuppression). Pseudomonas aeruginosa and Staphylococcus aureus are the most common bacterial causes; Candida or Aspergillus species are the most common fungal pathogens, though fungal infection (otomycosis) occurs less often than bacterial.

Clinical features

Ear pain, pruritus, and hearing loss; tenderness on manipulation of the tragus or auricle; discharge may be present. In severe cases, regional lymphadenitis or cellulitis of the pinna and adjacent skin. Otoscopy shows an inflamed external ear canal (erythema, oedema); fungal debris is typically visible in otomycosis.

Differentiate from perichondritis — inflammation of the pinna cartilage itself, distinct from otitis externa. Perichondritis characteristically spares the earlobe (which has no cartilage), whereas cellulitis does not. Perichondritis can lead to significant long-term ear disfigurement if untreated; early drainage of any associated abscess prevents anatomical damage to the cartilage — refer promptly if suspected. See Auricular Haematoma for the traumatic pinna-swelling differential.

Management

Keep the external ear canal as dry as possible. Remove discharge/debris by dry aural toilet, not water syringing — mechanical suction or, if performed by the patient/carer, dry-mopping with rolled tissue spears 6-hourly until the canal is dry. Debridement and dry aural toilet are the mainstays of treatment for fungal infection. Instil combination corticosteroid/antimicrobial ear drops after dry aural toilet; an ear wick can help drop administration if the canal is occluded. Oral antibiotics may be needed for fever, spread of inflammation to the pinna, folliculitis, or diabetes/immune compromise. Keep the ear dry during and for 2 weeks after treatment (earplugs or a shower/bathing cap when showering/swimming).

Ear drop choice:

• Fungal infection not suspected: Sofradex/Otodex (dexamethasone/framycetin/gramicidin), or Locacorten Vioform (flumethasone/clioquinol).
• Perforated TM, or TM couldn’t be visualised: Ciproxin HC — a quinolone-based drop is required; non-quinolone drops including Locacorten Vioform are ototoxic in the middle ear and not suitable once the TM is perforated or its integrity is uncertain.
• Fungal infection suspected: Locacorten Vioform, or Kenacomb/Otocomb Otic (triamcinolone/neomycin/gramicidin/nystatin).
• Systemic antibiotics required: di/flucloxacillin + ciprofloxacin, or cefalexin + ciprofloxacin, or clindamycin + ciprofloxacin.

Recurrent diffuse otitis externa

Prevent by keeping the external ear canal free of water — earplugs or a shower/bathing cap during showering/swimming; acetic acid + isopropyl alcohol ear drops (e.g. Aquaear) after water exposure (not during active infection). If recurrent infection occurs, manage as above.

Ear canal exostoses (bony growths, associated with repeated cold water exposure — “surfer’s ear”) are a structural risk factor for recurrent otitis externa via water trapping. Surgical repair is easier and safer while the eardrum can still be visualised — refer when exostoses cause recurrent infections, hearing loss, or pain. Simple preventive measures (e.g. dry-mopping after water exposure) reduce infection risk while awaiting review.

Necrotising (malignant) otitis externa

A rare complication of acute diffuse otitis externa — occurs where infection spreads to the cartilage and bone of the external ear canal and base of skull, usually caused by Pseudomonas aeruginosa. Consider the diagnosis in patients whose symptoms haven’t improved after treatment for acute diffuse otitis externa. Necrotising otitis externa is a key complication of AOE, commonly observed in diabetic and immunocompromised populations.

Demographics: elderly; diabetes; immunosuppressed (e.g. advanced HIV, chemotherapy for malignancy).

Clinical features: fever; severe persistent pain; visible granulation tissue; progressive cranial neuropathies.

Investigations: swab for culture and sensitivities (suspect Pseudomonas).

Management: urgent referral to ENT/infectious diseases. Antipseudomonal IV regimen: ceftazidime 2g three times daily, or tazocin (piperacillin/tazobactam) 4.5g four times daily, or ciprofloxacin 400mg three times daily.