{"id":2776,"date":"2018-01-17T17:17:14","date_gmt":"2018-01-17T22:17:14","guid":{"rendered":"http:\/\/phosdev.com\/todaysveterinarynurse\/?post_type=articles&p=2776"},"modified":"2022-02-15T21:32:34","modified_gmt":"2022-02-15T21:32:34","slug":"otitis-externa-inflammation-of-the-ear-canal","status":"publish","type":"post","link":"https:\/\/navc.sitepreview.app\/todaysveterinarynurse.com\/dermatology\/otitis-externa-inflammation-of-the-ear-canal\/","title":{"rendered":"Otitis Externa: Inflammation of the Ear Canal"},"content":{"rendered":"
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Otitis externa is a common condition that is frequently seen in specialty dermatology clinics and small animal general practices.<\/span>1,2<\/span><\/sup> It is defined as inflammation of the ear canal with or without involvement of the pinna.<\/span>1\u20133<\/span><\/sup> Otitis is often considered a final diagnosis, but it is merely a clinical sign. The many factors that can contribute to otitis need to be addressed so that initial infections do not progress to chronic changes, such as irreversible structural damage to the ear canal and cartilage.<\/span><\/p>\n

\"OTOSCOPIC<\/a>

Sandra Grable, conducts an examination of the ear canal. Photo courtesy of Bradley Leeb, University of Illinois<\/em><\/p><\/div>\n

Structures of the External Canal<\/h2>\n

The external ear consists of 3 structures: the pinna, the external ear canal (vertical and horizontal), and the tympanic membrane (TM). The pinna collects and transmits sound waves toward the TM.<\/span>4<\/span><\/sup> It is composed of auricular cartilage covered by skin. The vertical canal begins at the tragus, antitragus, and <\/span>anthelix<\/span> cartilages of the pinna; dogs may have few hairs at the entrance. Within the skin of the canals, hair follicles are present and the associated sebaceous and ceruminous glands produce cerumen. These secretions trap debris, protecting the canal and tympanum, and keep the TM flexible and moist.<\/span>1,4<\/span><\/sup> <\/span><\/p>\n

\"FIGURE<\/a>

FIGURE 1.<\/strong> Normal canine canal showing pars flaccida, pars tensa, manubrium of the malleus, and minimal cerumen.<\/p><\/div>\n

The TM, which is semitransparent and concave, separates the external and the middle ear. The angle of the TM differs between dogs and cats: 30 to 45 in dogs and 90 in cats.<\/span>1,4\u20136<\/span><\/sup> It has 2 distinct areas: the pars <\/span>flaccida<\/span> and the pars <\/span>tensa<\/span> (<\/span>F<\/span>IGURE<\/span> 1<\/span><\/strong>). The pink, triangular portion that lies dorsally is the pars <\/span>flaccida<\/span>, which supplies blood to the pars <\/span>tensa<\/span>. The pars <\/span>tensa<\/span> is a thin, translucent or opaque region that stretches across the canal and may appear striated. The manubrium of the malleus is embedded in 1 of the 3 layers of the pars <\/span>tensa<\/span> and points rostral.<\/span>5,6<\/span><\/sup> This knowledge is helpful when viewing video otoscopy images of the TM to identify which ear you are observing.<\/span><\/p>\n

Classification of Otitis<\/h2>\n

Otitis externa is classified into 4 categories, which helps in identifying the problem: predisposing, primary,\u00a0<\/span>secondary, and perpetuating factors.<\/p>\n<\/div>\n<\/div>\n

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Predisposing Factors<\/span><\/h3>\n

The predisposing factors of otitis do not cause ear disease. They only make the animal more susceptible to it or a more severe disease. Predisposing factors may be conformational, obstructive, or iatrogenic; increased moisture in the ear canal is also a predisposing factor. <\/span><\/p>\n

Conformational factors<\/span><\/strong> are attributed to floppy pinnae, such as those seen in bloodhounds, cocker spaniels, and basset hounds. This ear conformation can create a warm, moist environment (increased humidity) due to insufficient ventilation, resulting in the potential for overgrowth of the normal commensal flora. Cats do not appear to be affected by conformational differences of the pinnae, as seen with the Scottish fold.<\/span>3<\/span><\/sup> Excessive hair in the canal, as seen in poodles and schnauzers, can also decrease ventilation and form hair mats that retain debris and create obstructions.<\/span>7<\/span><\/sup> <\/span>Shar-peis<\/span> have stenotic canals that may be predisposed to higher humidity levels and secretions, leading to overgrowth of normal microbial inhabitants.<\/span>1,7<\/span><\/sup> An increase in glandular tissue can lead to an increase in cerumen production and debris accumulation, which seems to be more common in cocker spaniels, springer spaniels, and Labrador retrievers.<\/span>1,7<\/span><\/sup><\/p>\n

Increased moistur<\/strong>e<\/span> in the ear canal can result from swimming, bathing, or high humidity. <\/span><\/p>\n

\"FIGURE<\/a>

FIGURE 2.<\/strong> Ceruminous gland adenoma in the canal of a dog.<\/p><\/div>\n

Obstructive factors may inhibit epithelial migration (self-cleansing mechanism of the canal), resulting in a secondary <\/span>Malassezia<\/span><\/em> species or bacterial infection from cerumen accumulation.<\/span>1,7<\/span><\/sup> For example, polyps and tumors (<\/span>FIGURE 2<\/span><\/strong>) can prevent drainage of exudate, which predisposes ears to secondary infections. Common ear tumors include ceruminous and sebaceous gland tumors, inflammatory polyps, squamous cell carcinomas, mast cell tumors, and histiocytomas.<\/span>1,7<\/span><\/sup> <\/span><\/p>\n

Iatrogenic factors<\/span><\/strong> include hair plucking and trauma from overaggressive cleaning with cotton swabs, a common predisposition in cats.<\/span>3<\/span><\/sup> Hair plucking is standard grooming practice for dogs with excessive hairs in the canal, but it can damage the epithelial lining. Hair plucking is contraindicated in the normal ear because it can cause inflammation and predispose the animal to infection. In some cases, it may be indicated to prevent and manage otitis.<\/span>1,7<\/span><\/sup> <\/span><\/p>\n

<\/strong>BOX 1<\/strong> Primary Factors of Otitis1,8<\/sup><\/div>
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