Infections of the ear and associated structures can involve both the middle and the external ear, including the skin, cartilage, periosteum, ear canal, and tympanic and mastoid cavities. Both viruses and bacteria are known causes of these infections, some of which result in significant morbidity if not treated appropriately.
INFECTIONS OF EXTERNAL EAR STRUCTURES
Infections involving the structures of the external ear are often difficult to differentiate from noninfectious inflammatory conditions with similar clinical manifestations. Clinicians should consider inflammatory disorders as possible causes of external ear irritation, particularly in the absence of local or regional adenopathy. Aside from the more salient causes of inflammation, such as trauma, insect bite, and overexposure to sunlight or extreme cold, the differential diagnosis should include less common conditions such as autoimmune disorders (e.g., lupus or relapsing polychondritis) and vasculitides (e.g., granulomatosis with polyangiitis).
Auricular cellulitis is an infection of the skin overlying the external ear and typically follows minor local trauma. It presents as the typical signs and symptoms of cellulitis, with tenderness, erythema, swelling, and warmth of the external ear (particularly the lobule) but without apparent involvement of the ear canal or inner structures. Treatment consists of warm compresses and oral antibiotics such as cephalexin or dicloxacillin that are active against typical skin and soft tissue pathogens (specifically, S. aureus and streptococci). IV antibiotics such as a first-generation cephalosporin (e.g., cefazolin) or a penicillinase-resistant penicillin (e.g., nafcillin) occasionally are needed for more severe cases, with consideration of MRSA if either risk factors or failure of therapy point to this organism.
Perichondritis, an infection of the perichondrium of the auricular cartilage, typically follows local trauma (e.g., piercings, burns, or lacerations). Occasionally, when the infection spreads down to the cartilage of the pinna itself, patients may develop chondritis. The infection may closely resemble auricular cellulitis, with erythema, swelling, and extreme tenderness of the pinna, although the lobule is less often involved in perichondritis. The most common pathogens are P. aeruginosa and S. aureus, although other gram-negative and gram-positive organisms occasionally are involved. Treatment consists of systemic antibiotics active against both P. aeruginosa and S. aureus. An antipseudomonal penicillin (e.g., piperacillin) or a combination of a penicillinase-resistant penicillin and an antipseudomonal quinolone (e.g., nafcillin plus ciprofloxacin) is typically used. Incision and drainage may be helpful for culture and for resolution of infection, which often takes weeks. When perichondritis fails to respond to adequate antimicrobial therapy, clinicians should consider a noninfectious inflammatory etiology such as relapsing polychondritis.
The term otitis externa refers to a collection of diseases involving primarily the auditory meatus. Otitis externa usually results from a combination of heat and retained moisture, with desquamation and maceration of the epithelium of the outer ear canal. The disease exists in several forms: localized, diffuse, chronic, and invasive. All forms are predominantly bacterial in origin, with P. aeruginosa and S. aureus the most common pathogens.
Acute localized otitis externa (furunculosis) can develop in the outer third of the ear canal, where skin overlies cartilage and hair follicles are numerous. As in furunculosis elsewhere on the body, S. aureus is the usual pathogen, and treatment typically consists of an oral antistaphylococcal penicillin (e.g., dicloxacillin or cephalexin), with incision and drainage in cases of abscess formation.
Acute diffuse otitis externa is also known as swimmer’s ear, although it can develop in patients who have not recently been swimming. Heat, humidity, and the loss of protective cerumen lead to excessive moisture and elevation of the pH in the ear canal, which in turn lead to skin maceration and irritation. Infection may then follow; the predominant pathogen is P. aeruginosa, although other gram-negative and gram-positive organisms—and rarely yeasts—have been recovered from patients with this condition. The illness often starts with itching and progresses to severe pain, which is usually elicited by manipulation of the pinna or tragus. The onset of pain is generally accompanied by the development of an erythematous, swollen ear canal, often with scant white, clumpy discharge. Treatment consists of cleansing the canal to remove debris and enhance the activity of topical therapeutic agents—usually hypertonic saline or mixtures of alcohol and acetic acid. Inflammation can also be decreased by adding glucocorticoids to the treatment regimen or by using Burow’s solution (aluminum acetate in water). Antibiotics are most effective when given topically. Otic mixtures provide adequate pathogen coverage; these preparations usually combine neomycin with polymyxin, with or without glucocorticoids. Systemic antimicrobial agents typically are reserved for severe disease or infections in immunocompromised hosts.
Chronic otitis externa is caused primarily by repeated local irritation, most commonly arising from persistent drainage from a chronic middle-ear infection. Other causes of repeated irritation, such as insertion of cotton swabs or other foreign objects into the ear canal, can lead to this condition, as can rare chronic infections such as syphilis, tuberculosis, and leprosy. Chronic otitis externa typically presents as erythematous, scaling dermatitis in which the predominant symptom is pruritus rather than pain; this condition must be differentiated from several others that produce a similar clinical picture, such as atopic dermatitis, seborrheic dermatitis, psoriasis, and dermatomycosis. Therapy consists of identifying and treating or removing the offending process, although successful resolution is frequently difficult.
Invasive otitis externa, also known as malignant or necrotizing otitis externa, is an aggressive and potentially life-threatening disease that occurs predominantly in elderly diabetic patients and other immunocompromised persons. The disease begins in the external canal as a soft tissue infection that progresses slowly over weeks to months and often is difficult to distinguish from a severe case of chronic otitis externa because of the presence of purulent otorrhea and an erythematous swollen ear and external canal. Severe, deep-seated otalgia, frequently out of proportion to findings on examination, is often noted and can help differentiate invasive from chronic otitis externa. The characteristic finding on examination is granulation tissue in the posteroinferior wall of the external canal, near the junction of bone and cartilage. If left unchecked, the infection can migrate to the base of the skull (resulting in skull-base osteomyelitis) and onward to the meninges and brain, with a high mortality rate. Cranial nerve involvement is seen occasionally, with the facial nerve usually affected first and most often. Thrombosis of the sigmoid sinus can occur if the infection extends to the area. CT, which can reveal osseous erosion of the temporal bone and skull base, can be used to help determine the extent of disease, as can gallium and technetium-99 scintigraphy studies. P. aeruginosa is by far the most common offender, although S. aureus, Staphylococcus epidermidis, Aspergillus, Actinomyces, and some gram-negative bacteria also have been associated with this disease. In all cases, the external ear canal should be cleansed and a biopsy specimen of the granulation tissue within the canal (or of deeper tissues) obtained for culture of the offending organism. IV antibiotic therapy should be given for a prolonged course (6–8 weeks) and directed specifically toward the recovered pathogen. For P. aeruginosa, the regimen typically includes an antipseudomonal penicillin or cephalosporin (e.g., piperacillin or cefepime), often with an aminoglycoside or a fluoroquinolone, the latter of which can even be administered orally given its excellent bioavailability. In addition, antibiotic drops containing an agent active against Pseudomonas (e.g., ciprofloxacin) are usually prescribed and are combined with glucocorticoids to reduce inflammation. Cases of invasive Pseudomonas otitis externa recognized in the early stages can sometimes be treated with oral and otic fluoroquinolones alone, albeit with close follow-up. Extensive surgical debridement, once an important component of the treatment approach, is now rarely indicated.
In necrotizing otitis externa, recurrence is documented up to 20% of the time. Aggressive glycemic control in diabetics is important not only for effective treatment but also for prevention of recurrence. The role of hyperbaric oxygen has not been clearly established.
INFECTIONS OF MIDDLE-EAR STRUCTURES
Otitis media is an inflammatory condition of the middle ear that results from dysfunction of the eustachian tube in association with a number of illnesses, including URIs and chronic rhinosinusitis. The inflammatory response in these conditions leads to the development of a sterile transudate within the middle ear and mastoid cavities. Infection may occur if bacteria or viruses from the nasopharynx contaminate this fluid, producing an acute (or sometimes chronic) illness.
Acute otitis media results when pathogens from the nasopharynx are introduced into the inflammatory fluid collected in the middle ear (e.g., by nose blowing during a URI). Pathogenic proliferation in this space leads to the development of the typical signs and symptoms of acute middle-ear infection. The diagnosis of acute otitis media requires the demonstration of fluid in the middle ear (with tympanic membrane [TM] immobility) and the accompanying signs or symptoms of local or systemic illness (Table 20-2).
TABLE 20-2GUIDELINES FOR THE DIAGNOSIS AND TREATMENT OF ACUTE OTITIS MEDIA ||Download (.pdf) TABLE 20-2 GUIDELINES FOR THE DIAGNOSIS AND TREATMENT OF ACUTE OTITIS MEDIA
|ILLNESS SEVERITY ||DIAGNOSTIC CRITERIA ||TREATMENT RECOMMENDATIONS |
|Mild to moderate ||>2 yrs or 6 mo to 2 yrs without middle-ear effusion ||Observation alone (deferring antibiotic therapy for 48–72 h and limiting management to symptom relief) |
| || |
<6 mo; or
6 mo to 2 yrs with middle-ear effusion (fluid in the middle ear, evidenced by decreased TM mobility, air/fluid level behind TM, bulging TM, purulent otorrhea) and acute onset of signs and symptoms of middle-ear inflammation, including fever, otalgia, decreased hearing, tinnitus, vertigo, erythematous TM; or
>2 yrs with bilateral disease, TM perforation, high fever, immunocompromise, emesis
Amoxicillin, 80–90 mg/kg qd (up to 2 g) PO in divided doses (bid or tid); or
Cefdinir, 14 mg/kg qd PO in 1 dose or divided doses (bid); or
Cefuroxime, 30 mg/kg qd PO in divided doses (bid); or
Azithromycin, 10 mg/kg qd PO on day 1 followed by 5 mg/kg qd PO for 4 d
Exposure to antibiotics within 30 d or recent treatment failurea,b:
Amoxicillin, 90 mg/kg qd (up to 2 g) PO in divided doses (bid), plus clavulanate, 6.4 mg/kg qd PO in divided doses (bid); or
Ceftriaxone, 50 mg/kg IV/IM qd for 3 d; or
Clindamycin, 30–40 mg/kg qd PO in divided doses (tid)
|Severe || |
As above, with temperature ≥39.0°C (102°F); or
Moderate to severe otalgia
Amoxicillin, 90 mg/kg qd (up to 2 g) PO in divided doses (bid), plus clavulanate, 6.4 mg/kg qd PO in divided doses (bid); or
Ceftriaxone, 50 mg/kg IV/IM qd for 3 d
Exposure to antibiotics within 30 d or recent treatment failurea,b
Ceftriaxone, 50 mg/kg IV/IM qd for 3 d; or
Clindamycin, 30–40 mg/kg qd PO in divided doses (tid);
Consider tympanocentesis with culture
Acute otitis media typically follows a viral URI. The causative viruses (most commonly RSV, influenza virus, rhinovirus, and enterovirus) can themselves cause subsequent acute otitis media; more often, they predispose the patient to bacterial otitis media. Studies using tympanocentesis have consistently found S. pneumoniae to be the most important bacterial cause, isolated in up to 35% of cases. H. influenzae (nontypable strains) and M. catarrhalis also are common bacterial causes of acute otitis media, and concern is increasing with MRSA as an emerging etiologic agent. Viruses, such as those mentioned above, have been recovered either alone or with bacteria in 17–40% of cases.
Fluid in the middle ear is typically demonstrated or confirmed with pneumatic otoscopy. In the absence of fluid, the TM moves visibly with the application of positive and negative pressure, but this movement is dampened when fluid is present. With bacterial infection, the TM can also be erythematous, bulging, or retracted and occasionally can perforate spontaneously. The signs and symptoms accompanying infection can be local or systemic, including otalgia, otorrhea, diminished hearing, and fever. Erythema of the TM is often evident but is nonspecific as it frequently is seen in association with inflammation of the upper respiratory mucosa. Other signs and symptoms occasionally reported include vertigo, nystagmus, and tinnitus.
TREATMENT Acute Otitis Media
There has been considerable debate on the usefulness of antibiotics for the treatment of acute otitis media. A higher proportion of treated than untreated patients are free of illness 3–5 days after diagnosis. The difficulty of predicting which patients will benefit from antibiotic therapy has led to different approaches. In the Netherlands, for instance, physicians typically manage acute otitis media with initial observation, administering anti-inflammatory agents for aggressive pain management and reserving antibiotics for high-risk patients, patients with complicated disease, or patients whose condition does not improve after 48–72 h. In contrast, many experts in the United States continue to recommend antibiotic therapy for children <6 months old in light of the higher frequency of secondary complications in this young and functionally immunocompromised population. However, observation without antimicrobial therapy is now the recommended option in the United States for acute otitis media in children >2 years of age and for mild to moderate disease without middle-ear effusion in children 6 months to 2 years of age. Treatment is typically indicated for patients <6 months old; for children 6 months to 2 years old who have middle-ear effusion and signs/symptoms of middle-ear inflammation; for all patients >2 years old who have bilateral disease, TM perforation, immunocompromise, or emesis; and for any patient who has severe symptoms, including a fever ≥39°C or moderate to severe otalgia (Table 20-2).
Because most studies of the etiologic agents of acute otitis media consistently document similar pathogen profiles, therapy is generally empirical except in those few cases in which tympanocentesis is warranted—e.g., cases refractory to therapy and cases in patients who are severely ill or immunodeficient. Despite resistance to penicillin and amoxicillin in roughly one-quarter of S. pneumoniae isolates, one-third of H. influenzae isolates, and nearly all M. catarrhalis isolates, outcome studies continue to find that amoxicillin is as successful as any other agent, and it remains the drug of first choice in recommendations from multiple sources (Table 20-2). Therapy for uncomplicated acute otitis media typically is administered for 5–7 days to patients ≥6 years old; longer courses (e.g., 10 days) should be reserved for patients with severe disease, in whom short-course therapy may be inadequate.
A switch in regimen is recommended if there is no clinical improvement by the third day of therapy, given the possibility of infection with a β-lactamase-producing strain of H. influenzae or M. catarrhalis or with a strain of penicillin-resistant S. pneumoniae. Decongestants and antihistamines are frequently used as adjunctive agents to reduce congestion and relieve obstruction of the eustachian tube, but clinical trials have yielded no significant evidence of benefit with either class of agents.
Recurrent acute otitis media
Recurrent acute otitis media (more than three episodes within 6 months or four episodes within 12 months) generally is due to relapse or reinfection, although data indicate that the majority of early recurrences are new infections. In general, the same pathogens responsible for acute otitis media cause recurrent disease; even so, the recommended treatment consists of antibiotics active against β-lactamase-producing organisms. Antibiotic prophylaxis (e.g., with trimethoprim-sulfamethoxazole [TMP-SMX] or amoxicillin) can reduce recurrences in patients with recurrent acute otitis media by an average of one episode per year, but this benefit is small compared with the high likelihood of colonization with antibiotic-resistant pathogens. Other approaches, including placement of tympanostomy tubes, adenoidectomy, and tonsillectomy plus adenoidectomy, are of questionable overall value in light of the relatively small benefit compared with the potential for complications.
In serous otitis media (otitis media with effusion), fluid is present in the middle ear for an extended period in the absence of signs and symptoms of infection. In general, acute effusions are self-limited; most resolve in 2–4 weeks. In some cases, however (in particular after an episode of acute otitis media), effusions can persist for months. These chronic effusions are often associated with significant hearing loss in the affected ear. The great majority of cases of otitis media with effusion resolve spontaneously within 3 months without antibiotic therapy. Antibiotic therapy or myringotomy with insertion of tympanostomy tubes typically is reserved for patients in whom bilateral effusion (1) has persisted for at least 3 months and (2) is associated with significant bilateral hearing loss. With this conservative approach and the application of strict diagnostic criteria for acute otitis media and otitis media with effusion, it is estimated that 6–8 million courses of antibiotics could be avoided each year in the United States.
Chronic suppurative otitis media is characterized by persistent or recurrent purulent otorrhea in the setting of TM perforation. Usually, there is also some degree of conductive hearing loss. This condition can be categorized as active or inactive. Inactive disease is characterized by a central perforation of the TM, which allows drainage of purulent fluid from the middle ear. When the perforation is more peripheral, squamous epithelium from the auditory canal may invade the middle ear through the perforation, forming a mass of keratinaceous debris (cholesteatoma) at the site of invasion. This mass can enlarge and has the potential to erode bone and promote further infection, which can lead to meningitis, brain abscess, or paralysis of cranial nerve VII. Treatment of chronic active otitis media is surgical; mastoidectomy, myringoplasty, and tympanoplasty can be performed as outpatient surgical procedures, with an overall success rate of ~80%. Chronic inactive otitis media is more difficult to cure, usually requiring repeated courses of topical antibiotic drops during periods of drainage. Systemic antibiotics may offer better cure rates, but their role in the treatment of this condition remains unclear.
Acute mastoiditis was relatively common among children before the introduction of antibiotics. Because the mastoid air cells connect with the middle ear, the process of fluid collection and infection is usually the same in the mastoid as in the middle ear. Early and frequent treatment of acute otitis media is most likely the reason that the incidence of acute mastoiditis has declined to only 1.2–2.0 cases per 100,000 person-years in countries with high prescribing rates for acute otitis media.
In countries such as the Netherlands, where antibiotics are used sparingly for acute otitis media, the incidence rate of acute mastoiditis is roughly twice that in countries like the United States. However, neighboring Denmark has a rate of acute mastoiditis similar to that in the Netherlands but an antibiotic-prescribing rate for acute otitis media more similar to that in the United States.
In typical acute mastoiditis, purulent exudate collects in the mastoid air cells (Fig. 20-1), producing pressure that may result in erosion of the surrounding bone and formation of abscess-like cavities that are usually evident on CT. Patients typically present with pain, erythema, and swelling of the mastoid process along with displacement of the pinna, usually in conjunction with the typical signs and symptoms of acute middle-ear infection. Rarely, patients can develop severe complications if the infection tracks under the periosteum of the temporal bone to cause a subperiosteal abscess, erodes through the mastoid tip to cause a deep neck abscess, or extends posteriorly to cause septic thrombosis of the lateral sinus.
Acute mastoiditis. Axial CT image shows an acute fluid collection within the mastoid air cells on the left.
Purulent fluid should be cultured whenever possible to help guide antimicrobial therapy. Initial empirical therapy usually is directed against the typical organisms associated with acute otitis media, such as S. pneumoniae, H. influenzae, and M. catarrhalis. Patients with more severe or prolonged courses of illness should be treated for infection with S. aureus and gram-negative bacilli (including Pseudomonas). Broad empirical therapy should be narrowed once culture results become available. Most patients can be treated conservatively with IV antibiotics; surgery (cortical mastoidectomy) is reserved for complicated cases and those in which conservative treatment has failed.