Pathogenesis (development of disease)
In otitis externa, inflammation of the ear canal occurs due to a variety of triggers.
The most common bacterial pathogens are Pseudomonas aeruginosa (58%) and Staphylococcus aureus (18%). Other pathogens may include: Proteus mirabilis (4%), Streptococcus pyogenes (2%), Escherichia coli (2%), Enterococcus sp. (2%), and Aspergillus sp. (2%).
Otitis externa diffusa: Pseudomonas aeruginosa, one of the most dangerous drinking water bacteria (wet germ), usually leads to a diffuse inflammatory edematous swelling of the external auditory canal after minor injuries (after ear rinsing or swimming).
Otitis externa circumscripta: The clinical picture is caused by hemolytic staphylococci, often also Staphylococcus aureus. This is indicated by redness and swelling with formation of lymph gland abscesses.
Otitis externa maligna: The dominant pathogen is Pseudomonas aeruginosa; if left untreated, osteomyelitis (inflammation of the bone marrow) of the base of the skull and meningitis (meningitis) can occur. The cause is usually diabetes mellitus or other diseases that lead to an immune deficiency.
Otitis externa can also be caused by mycosis (fungal disease) (otitis externa mycotica; moist otomycosis): mostly Aspergillus species are involved; often also Candida albicans.
In rare cases, viral diseases of the external ear also occur (e.g., herpes zoster oticus and herpes simplex).
Etiology (causes) of otitis externa diffusa
Behavioral causes
- Excessive “ear hygiene” (soapy water; manipulation with ear or cotton swabs), which can lead to microtraumatization of the ear canal skin
- Humid environment (especially visiting swimming pools).
- Irritation of the skin due to piercing, earrings, ear moulds.
- Allergic reactions / eczema against hair shampoos, hair sprays, cosmetics.
Causes due to disease
- Chronic otitis media (inflammation of the middle ear).
- Dermatoses (skin diseases) with involvement of the auditory canal (eg.atopic eczema (neurodermatitis), psoriasis).
- Diabetes mellitus and other metabolic diseases.
- Foreign body
- Auditory canal exostoses (ear canal growths)
- Auditory canal trauma
- Contact dermatitis (hair shampoos, earmolds from hearing aids, otologics/drugs used for ear disorders).
- Middle ear irritation
Other causes
- “Swimming pool infection”
- Use of hearing aids
Etiology (causes) of otitis externa circumscripta
Behavioral causes
- Infection with staphylococci from scratching or rubbing in the ear canal.
Etiology (causes) of otitis externa maligna
Disease-related causes
- Originating from inflammation of the ear canal.
- Diabetes mellitus or other diseases that lead to a weakening of the body’s defenses
Other causes
- After radiatio (radiotherapy)
