Sandbox: Otitis externa pathophysiology

# Overview
Otitis externa develops when the external ear canal becomes susceptible to infection due to a variety of causes. The primary pathogens responsible for otitis media are the bacteria Pseudomonas aeruginosa and Staphylococcus aureus. Sudden, invasive changes in humidity from a rapid intake of water into the ear canal can predispose the external ear to bacterial infection: The cerumen quantity in the ear canal decreases, weakening an important protective barrier in the ear; The epithelial surface of the skin begins to degrade, allowing easier infiltration by  bacterial; The pH value of the ear canal, usually maintained at 5.0 by a combination of the cerumen and the mechanical construction of the ear, increases and renders the ear more favorable to bacterial reproduction. Increased moisture in the ear canal can also lead to otitis externa caused by otomycosis. The primary fungal causes of otitis externa are Candida albicans and Aspergillus niger. The buildup of fungal debris in the ear canal epithelium leads to increasing pressure and inflammation. Surfer's ear, or exostosis of the ear canal raises the predisposition to otitis externa by rendering the ear canal more prone to trapping water and water-bourne pathogens. Localized physical trauma can cause Weakening of the ear canal epithelium and the lessening of cerumen, predisposing infection. Otitis externa is associated with infectious, inflammatory ear and head conditions. Gross pathology for otitis externa will include erythema of the ear canal, along with eczema-esque scaly, shedding of the skin. It also includes visible ear canal swelling, as well as potentially cellulitis of the pinna and otorrhea.

# Pathogenesis
Otitis externa develops when the external ear canal becomes susceptible to infection due to a variety of causes.

## Moisture-bourne infection
- Sudden, invasive changes in humidity from a rapid intake of water into the ear canal can predispose the external ear to infection.
Prolonged exposure to moisture causes swelling of the stratum corneum.
The cerumen quantity in the ear canal decreases, weakening an important protective barrier in the ear.
The epithelial surface of the skin begins to denegrate, allowing increased access for bacterial infection.
The pH value of the ear canal, usually maintained at 5.0 by a combination of the cerumen and the mechanical construction of the ear, increases and renders the ear more favorable to bacterial infection and otomycosis.
- Prolonged exposure to moisture causes swelling of the stratum corneum.
- The cerumen quantity in the ear canal decreases, weakening an important protective barrier in the ear.
- The epithelial surface of the skin begins to denegrate, allowing increased access for bacterial infection.
- The pH value of the ear canal, usually maintained at 5.0 by a combination of the cerumen and the mechanical construction of the ear, increases and renders the ear more favorable to bacterial infection and otomycosis.
- The bacteria Pseudomonas aeruginosa and Staphylococcus aureus are the most common opportunistic pathogens of otitis externa due to increased humidity.
- Increased moisture in the ear canal can also lead to otitis externa caused by otomycosis.
The primary fungal causes of otitis externa are Candida albicans and Aspergillus niger.
Spread of fungi results in inflammation in the ear canal.
The buildup of fungal debris in the ear canal epithelium leads to increasing pressure and inflammation.
Extensive use of topical antibiotic ear drops to treat bacterial otitis externa increases predisposition to otomycosis.
- The primary fungal causes of otitis externa are Candida albicans and Aspergillus niger.
- Spread of fungi results in inflammation in the ear canal.
- The buildup of fungal debris in the ear canal epithelium leads to increasing pressure and inflammation.
- Extensive use of topical antibiotic ear drops to treat bacterial otitis externa increases predisposition to otomycosis.
- For immunocompromised individuals, chronic or recurrent otitis externa from bacterial infection results from the spread of infection to the temporal bone.
Spread of infection may proceed through the temporal bone to the cranium.
- Spread of infection may proceed through the temporal bone to the cranium.

## Exostosis
- Surfer's ear, or exostosis of the ear canal raises the predisposition to otitis externa by rendering the ear canal more prone to trapping water and water-bourne pathogens.

## Dermatoses
- Localized physical trauma can lead to otitis externa from the following dermatoses:
Eczema
Seborrhea
Psoriasis
Contact dermatitis
- Eczema
- Seborrhea
- Psoriasis
- Contact dermatitis
- Weakening of the ear canal epithelium and the lessening of cerumen predisposes infection.

# Associated Conditions
- Otitis externa is associated with the following infectious, inflammatory ear and head conditions:
Otitis media
Osteitis
Osteomyelitis
Otorrhea
Otalgia
- Otitis media
- Osteitis
- Osteomyelitis
- Otorrhea
- Otalgia

# Gross Pathology
- Gross pathology for otitis externa will include erythema of the ear canal, along with eczema-esque scaly, shedding of the skin.
- Ear canal swelling will be visible.
- Cellulitis of the ] and otorrhea may also be present upon physical examination.
- A severe case of acute otitis externa, with visible narrowing of the external auditory channel and prominent amounts of exudate with swelling of the auricle.  Case provided by Dr. James Heilman.