Describe otitis externa with its types, causes and management.

Predisposing Factors and Classification

• Otitis externa is inflammation of the skin of the external auditory canal, with or without involvement of the pinna and tympanic membrane.
• It is among the commonest conditions in ENT practice and is essentially a dermatological disease occurring in an awkward place.
• The canal IS normally protected BY four mechanisms, and otitis externa follows when they are breached — which is why the predisposing factors matter more than the organism:

Diffuse Otitis Externa

• Diffuse otitis externa is generalised inflammation of the canal skin, and is the commonest form
• Organisms — pseudomonas aeruginosa is the commonest, followed by Staphylococcus aureus, proteus and other Gram-negative organisms; and often a mixed growth. Fungi in 10%
• Symptoms — pain, which is severe and out of proportion to the visible signs because the skin is tightly bound to periosteum in the bony canal with no room to swell; itching, which frequently precedes the pain and leads to the scratching that started it; discharge, scanty and watery at first; a blocked ear with conductive deafness if the canal occludes; and tenderness on chewing
• Signs — tragal tenderness and pain on moving the pinna, which are the cardinal signs and are absent in otitis media — this single distinction settles the diagnosis at the bedside; a red, oedematous, narrowed canal filled with debris; regional lymphadenopathy; and, in severe cases, spread to the pinna and face with cellulitis
• The drum must BE seen, even if this requires review after treatment, because otitis externa may be secondary to a discharging middle ear and the management is entirely different
• Treatment — the principles are clean, medicate, and treat the cause:
• Aural toilet is the single most important measure, and is frequently omitted. Debris must be removed under vision by suction or dry mopping.
• Topical therapy — antibiotic with steroid drops (ciprofloxacin, gentamicin, neomycin with hydrocortisone), or acidifying agents (2% acetic acid, aluminium acetate).
• A wick or ribbon gauze soaked in the medication should be inserted where the canal is too swollen for drops to enter, and changed daily. This is what converts a failing treatment into a working one
• Analgesia is essential and is under-prescribed; the pain is severe and patients frequently need more than paracetamol
• Systemic antibiotics are not routinely required, and are reserved for spreading cellulitis, fever, lymphadenopathy, diabetes or immunosuppression
• Keep the ear dry — no swimming, cotton wool with petroleum jelly while bathing, and nothing to be put into the ear
• Treat the underlying dermatosis, and stop any drop causing contact sensitivity.
• Tragal tenderness settles the diagnosis at the bedside, being present in otitis externa and absent in otitis media
• Pain is out of proportion to the signs because the skin is bound to periosteum in the bony canal and cannot swell
• Self-cleaning is the commonest precipitant, and removing the wax removes the protection that prevented the infection
• Pseudomonas is the commonest organism, followed by staphylococcus, and mixed growths are frequent
• Acidifying drops restore the natural pH, are cheap and effective, and do not select for resistance
• Insert a wick when the canal is too swollen for drops to enter, and change it daily until the swelling subsides
• Never syringe an inflamed canal; it adds the moisture and trauma that caused the condition in the first place
• Prescribe adequate analgesia; the pain is severe, is routinely underestimated and frequently needs more than paracetamol
• Systemic antibiotics are not routinely needed, and are reserved for cellulitis, fever, diabetes or immunosuppression
• See the drum before you finish, since a discharging middle ear may be the cause and needs entirely different treatment
• Suspect contact allergy if it worsens on treatment, and neomycin in ear drops is the commonest culprit
• Look for an underlying dermatosis; eczema, seborrhoeic dermatitis and psoriasis all present in the canal and need treating