What is the difference between otitis media and otitis externa?

Anatomical and Clinical Distinction Between Otitis Media and Otitis Externa

Otitis media is inflammation of the middle ear space behind the tympanic membrane, while otitis externa is infection of the external ear canal and auricle; the tympanic membrane serves as the anatomical dividing line between these two distinct conditions. 1, 2

Anatomical Location

Otitis Externa:

• Involves the skin and subcutaneous tissue of the external auditory canal, often extending to the auricle 2
• Occurs anterior to (outside of) the tympanic membrane 1
• Affects the ear canal that extends from the auricle to the eardrum 1

Otitis Media:

• Involves the middle ear cavity, which lies posterior to (behind) the tympanic membrane 1
• Encompasses the space containing the ossicles (malleus, incus, and stapes) 1
• Connected to the nasopharynx via the Eustachian tube 1

Pathophysiology

Otitis Externa:

• Results from direct infection of the ear canal skin, typically following trauma, moisture exposure, or loss of protective cerumen 2, 3
• Commonly called "swimmer's ear" due to water exposure as a precipitating factor 4
• Does not involve Eustachian tube dysfunction 2

Otitis Media:

• Results from Eustachian tube dysfunction that prevents middle ear drainage and ventilation 1, 5
• Nearly always preceded by viral upper respiratory infection that causes nasopharyngeal and Eustachian tube inflammation 1
• Bacterial pathogens translocate from the nasopharynx through the dysfunctional Eustachian tube 1

Microbiology

Otitis Externa:

• Pseudomonas aeruginosa and Staphylococcus aureus are the predominant pathogens 2
• These organisms thrive in the moist, warm environment of the external canal 3

Otitis Media:

• Streptococcus pneumoniae, non-typeable Haemophilus influenzae, and Moraxella catarrhalis are the three dominant bacterial otopathogens 1, 6
• Approximately 5% of cases are caused by viruses alone 1
• Bacterial biofilms may form in chronic cases 1

Clinical Presentation

Otitis Externa:

• Ear pain with manipulation of the auricle or tragus is characteristic 2, 3
• Tenderness when touching the external ear 2
• Ear discharge (otorrhea) visible in the external canal 2
• Fever may be present 2
• The tympanic membrane remains intact and may appear normal if visualized 2, 4

Otitis Media (Acute):

• Rapid onset of ear pain (otalgia) or ear pulling in infants 1, 7
• Bulging tympanic membrane is the hallmark finding 1, 7
• Fever in approximately 69% of cases (absent in 31%) 7
• Irritability in infants and toddlers 1, 7
• Otorrhea only if tympanic membrane perforates 1
• No pain with external ear manipulation (distinguishes from otitis externa) 2

Diagnostic Examination

Otitis Externa:

• Examination reveals erythema and edema of the external canal skin 3
• Pain elicited by pulling the auricle or pressing the tragus 3
• Debris and discharge visible in the canal 3
• Tympanic membrane may be difficult to visualize due to canal swelling but is typically normal 4

Otitis Media:

• Requires pneumatic otoscopy to assess tympanic membrane position, color, translucency, and mobility 7
• Bulging tympanic membrane with impaired mobility has 96% specificity for acute otitis media 7
• Cloudy tympanic membrane with impaired mobility has 95% sensitivity and 85% specificity for middle ear effusion 7
• Distinct erythema combined with bulging or effusion confirms inflammation 7
• No external ear tenderness 1, 2

Critical Diagnostic Pitfall

The key clinical distinction is that acute otitis media diagnosis explicitly requires ruling out otitis externa as the cause of ear discharge. 1 When otorrhea is present, clinicians must determine whether it originates from:

• The external canal (otitis externa), or
• The middle ear through a perforated tympanic membrane (acute otitis media with perforation) 1

This distinction fundamentally changes both the causative organisms and the treatment approach 2, 4.

Age Distribution

Otitis Externa:

• Lifetime prevalence of 10% across all ages 3
• Can occur at any age when predisposing factors are present 3, 4

Otitis Media:

• Peak incidence in the first year of life (45.3 episodes per 100 children per year) 7
• Highest rates in children 1-4 years of age (61 episodes per 100 children per year) 7
• By age 3, 50-85% of children will have had at least one episode 7
• Predominantly a pediatric disease due to immature Eustachian tube anatomy 5

Treatment Approach

Otitis Externa:

• Topical antibiotics (covering Pseudomonas) and corticosteroids are first-line 2, 3
• Cleansing of the external auditory canal 3
• Oral antibiotics only if infection spreads beyond the canal or in immunocompromised/diabetic patients 2, 3

Otitis Media:

• Systemic antibiotics (covering S. pneumoniae, H. influenzae, M. catarrhalis) for children under 2 years 7
• Observation option for selected older children with mild disease 1
• Pain management is essential regardless of antibiotic use 1
• Topical ear drops are not effective because the tympanic membrane blocks drug penetration to the middle ear 1