Otitis Externa Lecture Review

Otitis Externa

Introduction

• Otitis externa, also known as external otitis or swimmer's ear, is defined as inflammation of the external auditory canal.
• Common causes include infectious, allergic, and dermatologic diseases, with acute bacterial infection being the most frequent.
• The focus is on the pathogenesis, clinical features, and diagnosis of acute otitis externa (AOE) in adults.

Epidemiology

• AOE can affect all age groups.
• Approximately 10 percent of people will develop AOE in their lifetime.
• Incidence is higher in the summer months, possibly due to increased humidity and water activities.

Anatomy

• The external auditory canal includes cartilaginous and bony portions.
• The isthmus is the narrowest region of the ear canal.
• The outer cartilaginous portion contains cerumen glands, sebaceous glands, and hair follicles.
• The inner bony portion features thin skin in proximity to the periosteum.
• Boundaries of the ear canal are relevant to potential complications.
• Fissures of Santorini may play a role in the spread of infection.
• The external auditory canal measures approximately 2.5 cm in length and 7 to 9 mm in width, extending from the conchal cartilage of the auricle to the tympanic membrane.
• The outer cartilaginous portion occupies approximately one-third of the canal, while the medial bony portion occupies the other two-thirds.
• The junction between these portions is termed the isthmus, which is the narrowest region of the ear canal.
• The outer cartilaginous portion is lined by thicker skin containing cerumen glands (a modified apocrine type gland), sebaceous glands, and hair follicles, where cerumen is formed.
• The inner osseous portion of the canal contains thin skin without subcutaneous tissue.
• The inferior tympanic recess is a small depression in the inferior medial aspect of the ear canal, adjacent to the tympanic membrane; debris can collect in this area and cause or perpetuate infection.

Pathogenesis

• Breakdown of the skin-cerumen barrier is the initial step in AOE development.
• Inflammation and edema lead to pruritus and further injury from scratching.
• Changes in cerumen, impaired epithelial migration, and increased pH create a favorable environment for organisms.

Risk Factors

• Swimming and water exposure are risk factors.
• Trauma from excessive cleaning or scratching.
• Occlusive ear devices like hearing aids and earphones.
• Allergic contact dermatitis.
• Dermatologic conditions such as psoriasis and atopic dermatitis.
• Prior radiation therapy.

Microbiology

• Most common bacterial pathogens are Pseudomonas aeruginosa and Staphylococcus aureus.
• Other gram-positive and gram-negative bacteria can also be involved.
• Anaerobic pathogens are present in a significant percentage of cases.
• Fungal infections (otomycosis) account for a smaller percentage and often occur after antibiotic treatment.
• Polymicrobial infections are also common.

Acute External Otitis Microbiology

• Aerobic Bacteria:
  • Pseudomonas: 41%
  • Staphylococcus aureus: 15%
• Anaerobic Bacteria:
  • Peptostreptococcus: 22%
  • Bacteroides: 11%
• Fungal: 6.5%
• Mixture of Organisms:
  • Aerobic only: 67%
  • Anaerobic only: 17%
  • Mixed aerobic and anaerobic: 9%
• Number of Organisms:
  • Single organism: 65%
  • 2 organisms: 24%
  • More than 3 organisms: 11%

Clinical Features

• Common symptoms include ear pain, pruritus, discharge, and hearing loss.
• It is important to gather patient history regarding previous ear issues, trauma, water exposure, and use of ear devices.

Physical Examination Findings

• Tenderness with tragal pressure or auricle manipulation.
• Edematous and erythematous ear canal.
• Presence of debris or cerumen.
• Possible erythema of the tympanic membrane.
• Mobility of the tympanic membrane with pneumatic insufflation.

Diagnosis

• Diagnosis is primarily clinical, based on history and physical examination.
• American Academy of Otolaryngology-Head and Neck Surgery guidelines define diffuse acute otitis externa.
• Cultures are generally reserved for severe cases, recurrent infections, chronic otitis externa, immunocompromised patients, post-ear surgery infections, and cases not responding to initial treatment.

Differential Diagnosis

• Otomycosis: Fungal infection with characteristic appearance. Key symptoms include itching, discomfort, and discharge.
• Contact Dermatitis: Persistent edema and erythema despite AOE treatment, often with intense itching and potential extension to the conchal cartilage. Common causes include ototopical medications, cosmetics, and shampoos.
• Chronic Suppurative Otitis Media (CSOM): May present with a draining ear but usually has a history of ear disease and milder ear canal symptoms. Tympanic membrane perforation or retraction pocket may be present.
• Carcinoma of the Ear Canal: Rare but should be considered with abnormal tissue growth or lack of response to prolonged treatment. Symptoms may include mild pain and bloody otorrhea.
• Psoriasis: Can involve the external ear canal, causing redness and scaling.

Treatment

Cleaning the Ear Canal

• Essential first step in treatment.
• Removal of cerumen, desquamated skin, and purulent material facilitates healing and enhances penetration of topical ear drops.
• Performed using an otoscope with direct visualization, employing a loop-tipped ear curette or cotton swab.
• Irrigation with a 1:1 dilution of 3% hydrogen peroxide with water at body temperature can be used if the tympanic membrane (TM) is intact.
• Referral to otolaryngology is appropriate for cleaning if the TM is ruptured or cannot be fully visualized.

Treating the Infection

• Approach depends on the severity of AOE, presence of diabetes or immunocompromise, and TM status.

Intact Tympanic Membrane

• Mild Disease: Topical acetic acid-hydrocortisone is suggested. Topical antibiotics are generally not preferred for mild cases.
• Moderate Disease: Topical antibiotic with glucocorticoid is suggested (e.g., ciprofloxacin-hydrocortisone, ciprofloxacin-dexamethasone, or neomycin-polymyxin B-hydrocortisone). Fluoroquinolones are often preferred due to fewer side effects.
• Severe Disease: Topical antibiotic with glucocorticoid is suggested. Wick placement may be necessary if the canal is completely occluded. Oral antibiotics (e.g., fluoroquinolone) may be added for patients with fever. Cultures of ear canal drainage should be obtained.

Nonintact Tympanic Membrane or Unknown Status

• Topical fluoroquinolone (e.g., ciprofloxacin-dexamethasone, ciprofloxacin, ofloxacin) is suggested for a seven-day course.
• Avoid ototoxic preparations like aminoglycosides, alcohol, and acidic solutions.
• Systemic antibiotics are indicated for fever or cellulitis.
• Referral to ENT is recommended if no improvement after one week.

Patients with Cellulitis

• Dual therapy with topical and systemic antibiotics is suggested. Systemic antibiotic choice depends on the severity of cellulitis.

Immunocompromised Hosts

• Combined systemic and topical antibiotics are suggested regardless of severity. Referral to an otolaryngologist and possibly an infectious disease specialist is recommended for refractory cases.

Topical Otic Preparations: General Principles

• Deliver high concentration of medication with few side effects.
• Classes include antibiotics, antiseptics, glucocorticoids, and acidifying solutions.
• Selection depends on disease severity and TM status.

Pain Management

• Most patients with mild to moderate pain get relief with topical therapy.
• Oral NSAIDs (e.g., ibuprofen, naproxen) can be used for additional analgesia.
• Persistent pain in diabetic patients should raise suspicion for malignant otitis externa.

Patient Counseling

• Proper instillation of topical preparations is crucial.
• Tilt head, pull auricle upward, and fill the ear canal with drops (typically 4-6 for adults).
• Maintain position or use a cotton ball for 3-20 minutes after instillation.
• Protect ear from water during treatment using a petroleum jelly-coated cotton ball.
• Avoid swimming and water sports for 7-10 days.
• Disinfect and avoid wearing hearing aids and similar devices until symptoms subside.

Prevention of Recurrence

• Patient education on proper ear hygiene is essential.
• Avoid inserting foreign objects into the ear canal.
• For those in water sports: use ear plugs, shake ear dry, and use a blow dryer on a low setting.
• Alcohol and/or acetic acid drops may help dry the ear.
• Clean hearing aids regularly.

Clinical Follow-up and Indications for Referral

• Most patients improve within 36-48 hours, with full resolution in about six days.
• Follow-up timeframe depends on severity.
• Culture ear canal if no response to initial treatment.
• Refer to otolaryngologist for unresolved AOE, unrelenting pain, cranial nerve dysfunction, vertigo, suspicion of neoplasia or malignant otitis externa.
• Refer diabetic or immunocompromised patients with severe otitis externa or persistent unilateral ear pain.

Management of Contributing or Similar Conditions

• Otomycosis: Meticulous cleaning of the ear canal and topical antifungal therapy (e.g., clotrimazole 1% solution) are the mainstay of treatment. Systemic antifungals may be needed in some cases.
• Contact Dermatitis: Eliminate the causative agent, clean the ear, and use topical glucocorticoids.
• Malignant Otitis Externa: Requires systemic antipseudomonal antibiotics and urgent referral to otolaryngology and an infectious disease specialist.

Complications

• Periauricular Cellulitis: Erythema, edema, and warmth around the auricle.
• Malignant Otitis Externa (Necrotizing External Otitis): Severe, potentially fatal complication, mainly in older adults with diabetes or immunocompromised individuals, involving spread of infection to the skull base. Characterized by severe otalgia, otorrhea, granulation tissue, and potential cranial nerve palsies.

Necrotizing (malignant) external otitis (NEO)

• An invasive infection of the external auditory canal that can lead to skull base osteomyelitis.

• Typically occurs in older adults with diabetes mellitus.

• Infection spreads beyond the skin to soft tissue, cartilage, and bone of the temporal region and skull base.

• Risk factors in diabetics may include microangiopathy in the ear canal and increased pH in diabetic cerumen.

• Caused by P. aeruginosa in more than 95 percent of cases. Other organisms include Aspergillus species. Occasional reports of Staphylococcus aureus, Proteus mirabilis, Klebsiella oxytoca, Burkholderia cepacia, and Candida parapsilosis.