Otitis externa (外耳道炎)

Definition:

Inflammation of the skin of the external auditory meatus.

Aetiology:

Caused by either primary infection or contact sensitivity to topically applied substances such as cosmetics or antibiotics. Gram-negative organisms (e.g. Proteus, Pseudomonas) and fungi (e.g. Aspergillus) are often found. 

Precipitating factors include impacted cerumen, local trauma, middle ear discharge through a tympanic membrane perforation, swimming and skin conditions such as psoriasis and seborrheic dermatitis.

Clinical features:

Presents as otalgia, otorrhoea and deafness. The skin of the external auditory meatus is oedematous and inflamed. The meatus may be occluded with discharge and in fungal infections hypae may be seen. Traction on the pinna increases the otalgia, a sign not found in inflammatory conditions of the middle ear.

Management:

Debris must be removed from the meatus, either by dry mopping or by suction aided by the use of an operating microscope. A swab of the meatus is taken for bacteriology prior to the instillation of drops containing an antibiotic and steroid mixture. If the meatus is total occluded, an impregnated gauze wick may be inserted. In severe cases with cellulitis spreading onto the pinna systemic antibiotics are also needed.

Furunculosis of the external auditory meatus (外耳道癤)

Staphylococcal infection of hair follicles found in the lateral part of the meatus.

Clinical features:

Presents as severe otalgia exacerbated by traction on the pinna, with deafness if the meatus becomes occluded. The furuncle is often visible.

Management:

Most furuncles rupture spontaneously. Ribbon gauze impregnated with glycerin/ichthammol may be inserted daily into the meatus. Systemic flucloxacillin and analgesics are also needed.

Necrotizing (malignant) otitis externa (壞死性/惡性外耳炎)

A potentially fatal Pseudomonas infection of the external auditory meatus, with spread to the skull base. It occurs in elderly diabetics and also in patients with HIV/AIDS.

Clinical features:

Presents as severe otalgia, otorrhoea and deafness with progression to cranial nerve palsies (VII, IX, X, XI, XII) in advanced cases.

Management:

Treatment is by local surgery, usually mastoidectomy, combined with a prolonged course of specific antipseudomonal antibiotics. Skull base involvement and its response to treatment may be assessed by radioisotope scanning.