Otitis externa

Overview

•Otalgia - often severe and disproportionate; worsened by moving jaw or tragus

•Pruritus - common early symptom, often precedes pain

•Otorrhoea - purulent (bacterial) or white/fluffy (fungal)

•Tragal tenderness - hallmark sign; pain on pressing tragus or pulling pinna

•Canal erythema and oedema on otoscopy; tympanic membrane may not be visible

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Tragal tenderness distinguishes otitis externa from otitis media - in otitis media the ear canal and pinna are normal and pressing the tragus does not reproduce pain.

Investigations

•Otoscopy - visualise canal and confirm tympanic membrane integrity before prescribing topical drops

•Ear swab - not routine; use if treatment fails, fungal infection suspected, or immunocompromised

•CT temporal bones / MRI - if malignant otitis externa suspected (assess osteomyelitis and intracranial extension)

•Blood glucose / HbA1c - consider in severe or recalcitrant otitis externa to screen for diabetes

Management

•First-line (mild): acetic acid 2% ear drops/spray (e.g. EarCalm) - lowers canal pH; available OTC; also used prophylactically

•Second-line (moderate): topical antibiotic + corticosteroid - e.g. ciprofloxacin with dexamethasone, or neomycin with dexamethasone and acetic acid (Otomize)

•Third-line (severe/systemic features): oral flucloxacillin (or clarithromycin if penicillin allergic); discuss IV therapy with ENT

•Ear wick - used when canal too swollen for drops to penetrate; compressed sponge impregnated with topical antibiotic and steroid; removed after 24-48 hours once swelling reduces

•Fungal otitis externa (otomycosis): clotrimazole 1% solution 2-3 times daily for at least 14 days after clinical resolution

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Aminoglycosides (gentamicin, neomycin) are potentially ototoxic if the tympanic membrane is perforated. Always confirm drum integrity before prescribing. If the canal is too swollen to visualise the drum, do NOT prescribe aminoglycosides - refer to ENT for microsuction first.

Complications

•Conductive hearing loss - from canal occlusion (usually reversible with treatment)

•Canal stenosis - chronic otitis externa causes progressive fibrosis; can permanently narrow canal

•Pinna cellulitis - infection spreads to cartilage and surrounding soft tissue

•Mastoiditis - infection of mastoid airspace; complication of untreated/recurrent otitis media; presents with mastoid tenderness, anterior displacement of pinna, and pyrexia; treat with urgent IV antibiotics; surgical drainage if unresponsive or intracranial/extracranial complications develop

Malignant (necrotising) otitis externa

•Invasive infection extending beyond the EAC into soft tissue, cartilage, and temporal bone causing osteomyelitis

•Almost exclusively caused by Pseudomonas aeruginosa; occurs in diabetic or immunocompromised patients

•Features: severe pain out of proportion, granulation tissue at bony-cartilaginous junction, new facial nerve palsy

•Management: urgent ENT referral + IV anti-pseudomonal antibiotics (e.g. ciprofloxacin IV or piperacillin-tazobactam); surgical debridement may be needed

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Suspect malignant otitis externa in any diabetic or immunocompromised patient with otitis externa not responding to treatment - this is an ENT emergency. Mortality 10-21% with temporal bone involvement.