What are the different types of otitis externa?

Types of Otitis Externa

Otitis externa is classified into several distinct types: acute (diffuse) otitis externa, localized otitis externa (furunculosis), chronic otitis externa, necrotizing (malignant) otitis externa, fungal otitis externa (otomycosis), and otitis externa secondary to dermatologic conditions. 1, 2

Primary Classification

Acute (Diffuse) Otitis Externa

• Most common form, characterized by rapid onset of diffuse inflammation of the external auditory canal with otalgia, itching, canal edema, erythema, and otorrhea. 3, 4
• Primarily bacterial in etiology, with Pseudomonas aeruginosa and Staphylococcus aureus accounting for 98% of cases in North America. 2, 3
• Also known as "swimmer's ear" when occurring after water exposure due to conversion of the normal acidic canal environment to alkaline. 2, 5
• Tenderness with movement of the tragus or pinna is the classic diagnostic finding that distinguishes it from otitis media. 3, 4

Localized Otitis Externa (Furunculosis)

• Represents an infected hair follicle on the outer third of the ear canal, sometimes called localized otitis externa. 1
• Clinical findings include otalgia, otorrhea, localized tenderness, focal swelling, and pustular lesions. 1
• Staphylococcus aureus is the most common causative agent, requiring treatment with local heat, incision and drainage, or systemic antibiotics covering S. aureus. 1

Chronic Otitis Externa

• Often due to underlying skin disease rather than primary infection. 6, 3
• Frequently associated with allergies or inflammatory dermatologic conditions that require addressing the underlying cause rather than just antimicrobial therapy. 3

Necrotizing (Malignant) Otitis Externa

• A fulminant, life-threatening infection with extension beyond the external auditory canal involving osteomyelitis of the petrous bone. 2, 7, 6
• Occurs primarily in elderly diabetic or immunosuppressed patients. 8, 7, 6
• Presents with severe, unrelenting deep otalgia disproportionate to examination findings, persistent purulent otorrhea, and granulation tissue at the floor of the ear canal and bony-cartilaginous junction. 7
• May progress to headache, vertigo, meningismus, cranial nerve involvement (particularly facial nerve paralysis), and intracranial spread. 7
• Requires long-term antimicrobial therapy with antipseudomonal coverage, not just topical treatment. 7

Fungal Otitis Externa (Otomycosis)

• Less common than bacterial forms, generally caused by Aspergillus or Candida species. 2
• More prevalent in tropical countries, humid locations, after long-term topical antibiotic therapy, and in diabetic or immunocompromised patients. 8
• Topical antibiotic therapy is contraindicated as it is ineffective and may promote further fungal overgrowth. 8

Dermatologic Conditions Mimicking Otitis Externa

Contact Dermatitis

• Divided into irritant contact dermatitis (direct chemical damage from acids/alkalis affecting all individuals in dose-dependent manner) and allergic contact dermatitis (occurring only in susceptible individuals). 1
• Nickel is the most common contact allergen, affecting approximately 10% of women with pierced ears. 1
• Neomycin causes reactions in 5% to 15% of patients with chronic external otitis, with 13% of normal volunteers hypersensitive on patch testing. 1
• Management involves removing the sensitizing agent and applying topical steroids or calcineurin inhibitors (tacrolimus 0.1% ointment or pimecrolimus 1% cream). 1

Seborrheic Dermatitis

• Presents with greasy yellowish scaling, itching, and secondary inflammation from Malassezia yeast. 1
• More pronounced in patients with Down syndrome, HIV infection, and Parkinson's disease. 1
• Treatment includes topical antifungal medications to reduce yeast and topical anti-inflammatory medications. 1

Other Dermatologic Conditions

• Eczema, psoriasis, and discoid lupus erythematosus can involve the ear canal with characteristic skin lesions and often involvement of other body areas. 1

Viral Otitis Externa

• Rare but important causes include varicella, measles, or herpes virus. 1
• Herpes zoster oticus (Ramsay Hunt syndrome) causes vesicles on the external ear canal and posterior auricle, severe otalgia, facial paralysis, loss of taste on anterior two-thirds of tongue, and decreased lacrimation. 1
• Requires prompt systemic antiviral therapy and systemic steroids. 1

Critical Diagnostic Pitfall

The American Academy of Otolaryngology-Head and Neck Surgery emphasizes that clinicians must distinguish diffuse acute otitis externa from other causes of otalgia, otorrhea, and inflammation before initiating treatment. 1 Failure to properly differentiate can lead to inappropriate therapy, particularly confusing external otitis (H60 codes) with otitis media (H65-H67 codes). 2