Otitis externa pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Pathophysiology
Gross Pathology
The skin of the bony ear canal is unique, in that it is not movable but is closely attached to the bone, and it is almost paper thin. For these reasons it is easily abraded or torn by even minimal physical force. Inflammation of the ear canal skin typically begins with a physical insult, most often from injury caused by attempts at self-cleaning or scratching with cotton swabs, finger nails, hair pins, keys, or other small implements. Another causative factor for acute infection is prolonged water exposure in the forms of swimming or exposure to extreme humidity, which can compromise the protective barrier function of the canal skin, allowing bacteria to flourish; hence the name, "swimmer's ear". Densely impacted wax, usually caused by enthusiastic use of cotton swabs, can put enough pressure on the ear canal skin to injure it and initiate infection. A sensation of blockage or itching can prompt attempts to clean, scratch, or open the ear canal, which potentially worsens and perpetuates the condition. The cotton fibers of a swab are abrasive to the thin, fixed canal skin. Self-manipulative measures to improve the condition often make it worse and are to be discouraged, since it is a blind exercise that can result in significant injury to the ear. Production of wax by glands in the canal may be hindered by external otitis. The exact function(s) of cerumen (earwax) is a subject that is open to speculation, since there is very little research regarding its function. Some caretakers feel strongly that earwax has a protective function with respect to infection and that a little earwax in the ear canal is a good thing. A folliculitis of one of the hairs of the outer portion of the ear canal can be the start of a bout of external otitis.
It is well established that in most people the top layer of the ear canal skin normally migrates toward the ear opening, essentially sweeping the canal on a continuing basis. In other words, a normal ear canal is self-cleaning. This self-cleaning physiologic feature fails in some patients, especially in late life, and periodic cleaning by a physician can be necessary. The most controlled and least painful means of cleaning impacted wax or dead skin from the ear canal is by using a binocular surgical microscope, which frees the examiner's hands to instrument the ear and provides the magnification and depth perception needed to avoid traumatizing the delicate canal skin and eardrum.
Necrotizing External Otitis
There is an uncommon and serious form of external otitis called malignant or necrotizing external otitis, in which the infection extends beyond the confines of the ear canal and can involve the bone of the skull. Although the name of this condition contains the words external otitis it tends to follow a more severe and chronic clinical course and can lead to skull base osteomyelitis. Instead of being a condition that most people are subject to, necrotizing external otitis (also called malignant otitis externa) is a life-threatening disorder that only affects older individuals with diabetes and patients with major disorders of the immune system.[1]
References
- ↑ Beers S, Abramo T (2004). "Otitis externa review". Pediatr Emerg Care. 20 (4): 250–6. PMID 15057182.