What is the difference between acute localized otitis externa and acute diffuse otitis externa?

Acute Localized vs. Acute Diffuse Otitis Externa

Acute diffuse otitis externa is a bacterial cellulitis affecting the entire ear canal skin and subdermis with diffuse inflammation, while acute localized otitis externa (furunculosis) is a focal infection limited to a hair follicle or sebaceous gland, typically presenting as a discrete abscess or boil.

Key Distinguishing Features

Acute Diffuse Otitis Externa

• Distribution: Involves the entire length of the ear canal with widespread inflammation 1
• Pathophysiology: Represents a cellulitis of the ear canal skin and subdermis with diffuse edema and inflammation 1
• Causative organisms: Nearly all cases (98%) are bacterial, predominantly Pseudomonas aeruginosa (20-60%) and Staphylococcus aureus (10-70%), often as polymicrobial infection 1
• Clinical presentation:
  • Diffuse ear canal edema and erythema throughout the canal 1
  • Severe otalgia (70% of cases), itching (60%), or fullness (22%) 1
  • Intense tragal and pinna tenderness that is often disproportionate to visual findings 1
  • May have otorrhea, regional lymphadenitis, or cellulitis extending to pinna 1
• Treatment: Topical antimicrobial therapy is the definitive first-line treatment, with 65-90% clinical resolution within 7-10 days 2

Acute Localized Otitis Externa (Furunculosis)

• Distribution: Focal, localized infection confined to a specific area of the canal 3
• Pathophysiology: Infection of a hair follicle or sebaceous gland forming a discrete abscess or furuncle 1, 3
• Causative organisms: Primarily Staphylococcus aureus 3
• Clinical presentation:
  • Discrete, localized swelling or boil visible in the ear canal 3
  • Pain may be severe but is localized to the area of the furuncle 3
  • The inflammation is not diffuse throughout the canal 3
• Treatment: Local heat application and systemic antibiotics during the inflammatory stage; incision and drainage when an abscess has formed 3

Clinical Implications for Management

The distinction is critical because diffuse AOE responds to topical antimicrobial therapy alone in uncomplicated cases, while localized otitis externa (furunculosis) requires systemic antibiotics and potentially surgical drainage 2, 3.

Common Pitfall

The American Academy of Otolaryngology-Head and Neck Surgery guidelines specifically address diffuse acute otitis externa, not localized disease 1. Clinicians must recognize that furunculosis represents a different entity requiring different management—attempting to treat a furuncle with topical drops alone will likely fail, while treating diffuse AOE with oral antibiotics represents overtreatment 2, 3.

Diagnostic Approach

• Diffuse AOE: Requires rapid onset (within 48 hours) in the past 3 weeks with symptoms of ear canal inflammation AND signs including tragal/pinna tenderness OR diffuse canal edema and erythema 1
• Localized AOE: Look for a discrete, focal lesion rather than diffuse canal involvement; the furuncle may obstruct visualization of deeper canal structures 1, 3