Infections of the External Ear

CHAPTER 137 Infections of the External Ear



Joel Guss, Michael J. Ruckenstein



Key Points



• The external ear and ear canal are affected by various bacterial, fungal, and viral infections, and noninfectious inflammatory conditions.

• Meticulous débridement of the ear canal is a crucial first step in managing all infections.

• Most cases of external otitis should be managed with topical medications.

• Infections that have spread beyond the confines of the ear canal skin require culture-directed systemic antibiotics.

• Malignant or necrotizing otitis externa is a life-threatening infection that requires a high index of suspicion and proper selection of radiographic and nuclear studies for prompt diagnosis.

• Infection of the auricular cartilage can lead to significant cosmetic deformity and requires aggressive treatment with systemic antipseudomonal antibiotics and, in many cases, surgical débridement.

• Viral infections of the ear canal include zoster oticus and, most likely, bullous myringitis; both may be associated with sensorineural hearing loss.

• Keratosis obturans and external auditory canal cholesteatoma are two poorly understood disorders marked by accumulation of squamous debris and bony remodeling of the ear canal; both are treated by débridement, but occasionally require aggressive surgical management.


Applied Anatomy


The external ear consists of the auricle and the external ear canal. The auricle, with the exception of its lobule, is formed by a framework of elastic cartilage. The perichondrium is tightly bound to the cartilage on its lateral surface and more loosely bound to its medial surface. Sebaceous glands and hair follicles are found in the subcutaneous layer of the auricle. Adipose tissue is generally restricted to the lobule. Keratinizing squamous epithelium covers the auricle. The ear canal measures approximately 2.5 cm in length, with the anterior portion being approximately 6 mm longer than the posterior wall. The lateral one third of the canal possesses a cartilaginous skeleton, a subcutaneous layer containing hair follicles, sebaceous and apocrine glands, and a squamous epithelial surface layer. The hydrophobic, slightly acidic (pH 6.0 to 6.5) cerumen is formed by glandular secretions and sloughed epithelium in this portion of the canal.


Transverse slits on the floor of the cartilaginous canal (the fissures of Santorini) allow for spread of infection or neoplasms from the external canal to the soft tissues surrounding the ear canal. The osseous portion of the canal begins at the narrow isthmus and is formed mostly by the tympanic portion of the temporal bone and a thin layer of squamous epithelium continuous with the lateral surface of the tympanic membrane. It lacks a subcutaneous layer.


The skin of the ear canal possesses a unique, self-cleansing mechanism. The sloughed keratinous layer of tympanic membrane migrates in a centrifugal fashion to the ear canal. This migratory process continues from the medial to lateral portions of the osseous canal, where the sloughed epithelium is deposited into the cartilaginous portion of the canal and is extruded as a component of cerumen.



Otitis Externa



Definition


Otitis externa is an inflammatory (typically infectious) disorder of the external ear canal.



Incidence and Epidemiology


Acute otitis externa affects approximately 4 of every 1000 children and adults per year.1 Approximately 80% of cases occur in the summer, particularly in warm, humid environments.2 Other predisposing factors include anatomic obstructions of the ear canal (e.g., stenosis, exostoses, impacted cerumen), hearing aid or ear plug use, self-induced trauma (e.g., by cotton swabs), and swimming.



Pathogenesis



Bacterial


The initiating event is believed to be an abrogation of the hydrophobic ceruminous coating of the external canal.3 This event exposes the underlying epithelium to water and other contaminants, leading to edema and excoriation of the epithelial layer. These violations of the epithelium allow for bacterial infection. The resulting infection and inflammatory response lead to progressive erythema and edema of the epithelial and subcutaneous layers. These pathologic changes are associated with the symptoms of itching, pain, and otorrhea.



Fungal


Fungal infections of the external canal are generally considered to be opportunistic, occurring after treatment of bacterial infection. Superficial infection of the ear canal by yeast (Candida sp) can be seen in patients who use hearing aids. Aspergillus sp may induce a more aggressive infection, involving the epithelial and subcutaneous tissues (Fig. 137-1).


image

Figure 137-1. Otomycosis. This florid infection with Aspergillus flavus has infected the deep canal, with tufts of fungus crowned by white conidiophores.



Chronic


Chronic otitis externa represents different disease states with distinct etiologies, as follows:


• Allergic otitis externa may result from an allergic reaction to topical agents, most commonly neomycin. It manifests as a maculopapular eruption on the skin of the conchal bowl and ear canal.

• A contact dermatitis can result from contact with various agents, including hairsprays, shampoos, and hearing aid molds.

• Psoriasis or systemic dermatitides such as seborrhea can involve the ear canal. The chronic inflammatory reaction typically results in hyperkeratosis and lichenification of the ear canal skin.

• Granular otitis externa is thought to result from chronic infection of the ear canal by bacteria or fungi or both. The ear canal skin and tympanic membrane manifest granulation and excoriation.


Microbiology


Roland and Stroman2 evaluated the microbiology of otitis externa. The results of their study are summarized in Table 137-1. Pseudomonas aeruginosa was the most common bacteria responsible for infections. Staphylococcus sp were the next most common pathogens. Fungi were responsible for only 2% of cases, but may be more prominent in cases of persistent or chronic infection.


Table 137-1 Microbiology of Otitis Externa






























Organism %
Pseudomonas aeruginosa 40
Staphylococcus epidermidis 9
Staphylococcus aureus 8
Other Staphylococcus sp 8
Coryneform (diphtheroids) 9
Other gram-negative rods 9
Streptococcus, Enterococcus 4
Aspergillus, Candida 2

From Roland PS, Stroman DW. Microbiology of acute otitis externa. Laryngoscope. 2002;112:1166-1177.



Clinical Manifestations


Pain is a common symptom associated with bacterial infection. The pain may be severe and is exacerbated by manipulation of the auricle or the tragus. Itching may be experienced in early bacterial infections, and in fungal infections and in all forms of chronic otitis externa. Aural fullness and decreased hearing may be experienced in any case of otitis externa resulting in accumulation of debris in the ear canal. Otorrhea is more common in bacterial infections.


Examination of the canal may reveal the following findings:


1. An erythematous canal with scant discharge in cases of early bacterial otitis externa

2. An edematous canal filled with purulent-squamous debris in cases of well-established bacterial otitis externa

3. An accumulation of white debris sprouting hyphae best seen with the otologic microscope, typical of candidal otitis externa

4. An accumulation of a moist white plug dotted with black debris (“wet newspaper”) typical of Aspergillus niger

5. A maculopapular eruption on the conchal bowl and in the ear canal consistent with an allergic reaction to a topical agent (e.g., neomycin)

6. A thickened, erythematous canal associated with an allergic or contact dermatitis

7. Granulation tissue in the canal and on the tympanic membrane caused by chronic infection


Investigations


Investigations are rarely required for cases of otitis externa. Cultures for bacteria and fungus are indicated in cases of persistent or refractory infection, particularly to identify fungal infection. Special reference must be made to the value of sensitivities of the infectious organism to various antibiotics provided by laboratory culture tests. These sensitivities are based on expected tissue levels of systemically administered antibiotics. Sampling of otorrhea after administration of topical preparations has shown a concentration of antibiotic several orders of magnitude greater than can be obtained by systemic administration, however, even 8 hours after dosing.4 Organisms listed as “resistant” to a particular antibiotic are likely to be susceptible to the antibiotic when it is given topically. This is true for so-called resistant cases of Pseudomonas sp or methicillin-resistant Staphylococcus aureus. As long as the topical drop can reach the infected site, systemic antibiotics are unnecessary even in cases of infection by “resistant” bacteria.


Biopsy of the external auditory canal should be undertaken in cases of presumed otitis externa that do not respond to appropriate antimicrobial therapy. Biopsy is done to exclude malignancy, most commonly squamous cell carcinoma of the ear canal skin, which may manifest with otalgia and otorrhea and may be misdiagnosed as infection.



Treatment


Careful débridement of the ear canal in any case of otitis externa is crucial to facilitate clearance of the infectious organism and to allow topical medications to reach the target tissue. If the ear canal is so edematous that topical medication would not reach its medial extent, an ear wick may be inserted. Classically, the physician made these from strands of cotton. Currently available Merocel wicks (Medtronic, Inc., Jacksonville, FL) offer better absorption of the drug, however, and expand when wet to decrease canal edema substantially. Although unpopular in North America, good results can also be obtained by packing the ear canal with antibiotic-impregnated ribbon gauze.5


Acidification of the ear canal is toxic to many bacteria (including Pseudomonas) and fungi, and effectively treats many early infections. A homemade mixture of equal amounts of white vinegar and rubbing alcohol acidifies and dries the ear canal. Commercial solutions of acetic acid (VoSol) or acetic acid with aluminum acetate (Domeboro) also are available. Acidifying solutions may also be used prophylactically by at-risk patients, such as after swimming. A hair dryer on a low heat setting may be used to dry the ear canal gently.


Antibiotic drops remain the mainstay of treatment for otitis externa. The ideal drops possess the following properties:


1. Broad-spectrum coverage for pathogenic bacteria (see Table 137-1)

2. An acidic vehicle

3. No potential for ototoxicity, which is an important property in the case of a perforated tympanic membrane

4. No potential for allergic reactions

5. No deposition of precipitate from the drop

6. Low cost

7. A steroid to decrease edema more rapidly and, perhaps, alleviate pain more rapidly

No current drop possesses all these properties. For many years, the mainstay of treatment was a combination solution of polymyxin, neomycin, and hydrocortisone (PNH) (Cortisporin). This combination is available in solution and suspension, and is produced by various manufacturers. Polymyxin provides coverage against Pseudomonas; polymyxin and neomycin are effective against S. aureus and other gram-negative organisms.


Quinolone antibiotics are available in otic and ophthalmic solutions. They offer single-agent coverage for pathogenic bacteria, with virtually no risk of contact dermatitis or ototoxicity. Ofloxacin (Floxin) is available for treatment of external and middle ear disease and is equal to PNH in efficacy.6,7 Its main disadvantages are a neutral pH (6.2 to 6.8), the absence of a steroid, and expense. Ciprofloxacin is available as an otic preparation combined with hydrocortisone and as a newer formulation combined with the more potent dexamethasone (Cipro HC and Ciprodex). These solutions are acidic and contain a steroid. The hydrocortisone in Cipro HC may leave a precipitate in the canal, and both solutions are expensive.


When choosing a topical treatment of otitis externa, there is currently minimal clinical evidence to support the use of one solution over another. Existing literature is difficult to interpret because studies differ in their outcome measures and in the degree of aural toilet used. A systematic review of topical treatments by Rosenfeld and colleagues8 reached the following conclusions: (1) topical antimicrobial and topical antiseptic drops were superior to placebo; (2) a topical antiseptic (with a steroid in most cases) was as effective as a topical antibiotic; (3) topical quinolone and nonquinolone antibiotics were equally effective except in achieving a bacteriologic cure, where the quinolones were more effective; and (4) a topical antibiotic is as effective as a topical antibiotic and steroid preparation. Chapter 138 contains further information on costs and emerging resistance with quinolone ototopicals.


Fungal otitis externa can be treated with meticulous débridement and acidification of the ear. As with bacterial infection, topical treatment cures most cases, although recurrence rates are high. Clotrimazole 1% solution (Lotrimin) is available over the counter and provides broad-spectrum antifungal activity. Cresylate otic and ketoconazole ointment are effective as well.9 An alternative popular treatment is painting the canal and tympanic membrane with dyes that possess antifungal properties (e.g., gentian violet). Tolnaftate (Tinactin) solution can be used safely in the presence of a tympanic membrane perforation.10,11 Finally, persistent Aspergillus

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Jun 5, 2016 | Posted by in OTOLARYNGOLOGY | Comments Off on Infections of the External Ear

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