Chronic
external otitis may be divided into several diagnostic categories. Disposition for
psoriasis, seborrhoeic and
atopic eczema are main endogenous reasons. Exogenous pathogens for
external otitis are microbes and
allergens. There are numerous interrelations by coincidence of dispositional diseases, e.g.
psoriasis and
atopic eczema and by combination of exogenous and endogenous pathogens. This holds good for the yeast Pityrosporum ovale vs. orbiculare in seborrhoeic
eczema and for the susceptibility to contact (type IV) and respiratory (type I)
allergy in atopic individuals as well. Mycotic and bacterial, especially gram negative
external otitis are linked to predisposing factors like
eczema, long-term microbicidal
therapy, hot and humid environment. Contact allergic
external otitis may occur during long lasting local
therapy with various substances including vehicles, the most common
allergen being
neomycin. Mucosal
allergic reactions (Type I) in the upper respiratory tract may impair ventilation of the Eustachian tube and middle ear and therefore epithelial migration, as a drainage mechanism of the auditory canal. Examination should include functional assessment of the Eustachian tube and middle ear and
allergy testing (patch, prick test). Preparations for local
therapy should contain a limited number of constituents and avoid common
allergens.
Surgical procedures to reestablish ventilation of the middle ear are also a
therapy for chronic
external otitis.