How many kinds of otitis externa?

             The term otitis externa refers to a collection of diseases involving primarily the auditory meatus. Otitis externa usually results from a combination of heat, retained moisture, and desquamation and maceration of the outer canal epithelium. The disease exists in a number of forms, which are identified as localized, diffuse, chronic, or invasive. They are all 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 with furunculosis elsewhere on the body, S. aureus is the usual pathogen, and treatment typically consists of an oral antistaphylococcal penicillin (e.g., dicloxacillin), 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 the absence of 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 occur; the predominant pathogen is P. aeruginosa, although other gram-negative and grampositive organisms have been recovered from patients with this condition. The illness often starts with itching and progresses to severe pain, which is usually triggered by manipulation of the pinna or tragus. The onset of pain is usually 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 to enhance the activity of topical therapies—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.

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 cotton swabs or other foreign objects inserted into the ear canal, can lead to this condition, as can rare chronic infections such as syphilis, tuberculosis, or 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. 7 Infections of the URT 189

Invasive otitis externa, also known as “malignant” or “necrotizing” otitis externa, is an aggressive and potentially life-threatening disease that occurs predominantly in elderly diabetics and other immunocompromised patients. The disease begins in the external canal, 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 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 skullbase osteomyelitis) and on to the meninges and brain, with a high associated mortality rate. Cranial nerve involvement is occasionally seen, with the facial nerve usually affected first and most often. Thrombosis of the sigmoid sinus can occur if the infection extends to that 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 pathogen involved, although S. aureus, Staphylococcus epidermidis, Aspergillus, Actinomyces, and some gram-negative bacteria have been associated with this disease. Cleansing of the external canal and biopsy of the granulation tissue within the canal (or of deeper tissues) should be performed in all cases to isolate the offending organism in culture. Intravenous antibiotic therapy is directed specifically toward the recovered pathogen. For P. aeruginosa, the regimen typically includes an antipseudomonal penicillin or cephalosporin (e.g., piperacillin or ceftazidime) with an aminoglycoside. A fluoroquinolone antibiotic is frequently used in place of the aminoglycoside and can even be administered orally, given its excellent bioavailability. Antibiotic drops containing an agent active against Pseudomonas (e.g., ciprofloxacin) are also 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.

Source: Harrison_s_Principles_of_Internal_Medicine_16th_Edition