Otitis externa

Otitis externa (OE) refers to inflammation of the external auditory canal, which is most often the result of a local bacterial infection. Risk factors for OE include injury to the skin of the external auditory canal and/or exposure to water. OE is characterized by ear pain, discharge, and tragal tenderness. Otoscopy may reveal a furuncle (localized OE) or a red, edematous external auditory canal (diffuse OE). OE is primarily a clinical diagnosis. Treatment involves keeping the external auditory canal dry and administering fluoroquinolone and hydrocortisone ear drops. Systemic antibiotic therapy is usually indicated in immunosuppressed and/or diabetic patients who are at risk of a more severe variant called malignant otitis externa (MOE). MOE, which is almost always caused by Pseudomonas aeruginosa, may present with facial nerve palsy and is potentially fatal because it spreads rapidly to the base of the skull. Immediate referral and treatment with systemic antipseudomonal antibiotics are indicated.

• Most cases of otitis externa are infectious in origin.
  • Pathogens
    • Bacterial infections (most common cause of otitis externa)
      • Pseudomonas aeruginosa (∼ 40% of cases), commonly from swimming activities
      • Staphylococcus aureus, Proteus mirabilis, Escherichia coli
    • Fungal infections (less common): Aspergillus (accounts for 90% of all fungal otitis externa), Candida
    • Viral infections (rare): Herpes zoster, Influenza viruses
  • Risk factors
    • Injury to the skin of the external auditory canal; (e.g., cleaning, insertion of foreign objects such as hearing aids or earplugs, excessive itching)
    • Increased moisture in the external auditory canal (e.g., swimming, humid climate)
• Non-infectious forms of otitis externa are less common and include
  • Seborrheic otitis externa (associated with seborrheic dermatitis)
  • Eczematous otitis externa (a hypersensitivity reaction to pathogens or topical antibiotics)
  • Neurodermatitis (caused by compulsive/psychogenic scratching).

• Symptoms
  • Severe ear pain, particularly at night
  • Otorrhea
  • Intense itching in the external auditory canal
• Signs
  • The tragus is tender to touch
  • Pulling up and back on the auricle causes pain
  • Conductive hearing loss
  • Otoscopic findings
    • Localized OE: Furuncle
    • Diffuse OE: Edematous and reddened external auditory canal

Malignant otitis externa (necrotizing otitis externa) ^[1][2]

• Definition: necrotizing inflammation of the external auditory canal
• Etiology
  • Pathogen: Pseudomonas aeruginosa (95% of cases)
  • Risk factors:
    • Elderly patients with poorly controlled diabetes
    • Immunosuppression
• Clinical features
  • Severe ear pain
  • Red and swollen periauricular soft tissue
  • Otorrhea
  • Conductive hearing loss
  • Otoscopic findings: granulation tissue at the transition between the cartilaginous and the osseous part of the ear canal
• Complications
  • Facial nerve palsy
  • Osteomyelitis of the skull base → extradural abscess, venous sinus thrombosis, paralysis of other cranial nerves
• Diagnostics
  • Imaging
    • CT scan to identify bone destruction
    • MRI to identify intracranial extension (e.g., venous sinus thrombosis, cranial abscess)
    • Gallium-67 scan in order to monitor response to treatment
  • Biopsy: distinguishes malignant otitis externa from a tumor and helps optimize treatment
• Treatment
  • Prompt IV antibiotic therapy for several weeks
    • First-line: high-dose ciprofloxacin
    • Second-line: other antipseudomonal antibiotics (e.g., piperacillin-tazobactam, ticarcillin, cefepime, ceftazidime)
  • Surgical debridement is indicated for abscess drainage and removal of bony sequestrum
  • Topical antibiotic treatment (see “Therapy” below)
• Prognosis: The mortality rate is high even with appropriate antibiotic therapy

Malignant otitis externa is a severe infection that is often lethal.

• Otitis externa is primarily a clinical diagnosis.
• Check blood glucose levels to rule out diabetes
• Culture and sensitivity tests are not routinely performed; they may be indicated if antibiotic treatment is not effective.

Fungal otitis externa should be suspected when symptoms do not resolve with local and/or systemic antibiotic therapy (especially among immunocompromised and diabetic patients).

• Topical treatment (initial treatment of uncomplicated otitis externa)
  • Antibiotic eardrops (typically ofloxacin, ciprofloxacin, or gentamicin)
  • Topical preparations with corticosteroids (e.g., hydrocortisone, prednisolone) to control itching and inflammation
  • Aural toilet: clean the external auditory canal and keep it dry using an ear wick and/or astringents (e.g., mixture of isopropyl alcohol and acetic acid)
• Systemic treatment: oral ciprofloxacin (in addition to topical treatment)
  • Indications
    • Immunosuppression
    • Diabetes mellitus
    • Severe otitis externa with cellulitis of the face and neck
    • Topical administration of antibiotics is not possible (e.g., severe edema of the external auditory canal) or is ineffective.
  • NSAIDs for pain relief
  • Special patient groups: see “Antibiotics during pregnancy.”

• Indications
  • Recurrent episodes of otitis externa
  • Immunosuppression
  • Chronic dermatologic conditions such as atopic dermatitis and psoriasis
• Interventions
  • Frequent swimmers should keep the auricle and external auditory canal clean and dry.
    • Use a tight-fitting bathing cap.
    • Use a hairdryer at the lowest heat setting and not too close to the ear.
    • Consider use of acetic acid and/or alcohol-based ear drops to dry the ear and to re-acidify the ear canal.
  • Treat underlying chronic dermatologic conditions.
  • Hearing aids should be removed and cleaned regularly.
  • Recommend that the patient avoids manipulation of the ear canal (e.g., use of cotton buds to clean the ear).

References:^[3]

1. Dhingra PL, Dhingra S. Diseases of Ear, Nose and Throat. Elsevier ; 2014
2. Handzel O, Halperin D. Necrotizing (malignant) external otitis.. Am Fam Physician. 2003; 68 (2): p.309-12.
3. Otitis Externa: A Practical Guide to Treatment and Prevention. https://www.aafp.org/afp/2001/0301/p927.html. Updated: March 1, 2001. Accessed: April 29, 2020.