Otitis externa

What it is

Otitis externa is inflammation of the external auditory canal, diffuse or localized. On an aetiological basis it divides into an infective group and a reactive group. The infective group is bacterial — localized otitis externa, the furuncle; diffuse otitis externa; and malignant otitis externa — fungal, which is otomycosis, and viral, which is herpes zoster oticus and otitis externa haemorrhagica. The reactive group is eczematous otitis externa, seborrhoeic otitis externa and neurodermatitis. The organisms are bacterial in 99% — P. aeruginosa, S. aureus, E. coli — and fungal in the rest, Aspergillus and Candida.

Causes and risk

Swimming, the swimmer's ear, in a humid climate. Mechanical cleaning and aggressive scratching. Devices that occlude the ear canal: hearing aids and headphones. A narrow ear canal. Trauma. Dermatologic conditions such as psoriasis and atopic dermatitis, which is what makes it chronic. The furuncle is its own line: a localized skin infection involving one or more hair follicles of the outer ear canal, from S. aureus, and in recurrent furunculosis diabetes should be excluded.

The fungal infection of the ear canal, otomycosis, carries a risk list of its own: immunosuppression, for example HIV and diabetes; long-term antibiotic therapy; and residence in a hot, humid area. It is seen in the hot and humid climate of tropical and subtropical countries, and secondary fungal growth is also seen in patients using topical antibiotics for treatment of otitis externa or middle ear suppuration - so the ear that was given antibiotic drops and came back worse is the ear to look for it in.