Definition

Ot=ear + itis=inflammation.

Externa= Of the external ear or pinna.

Clinical Signs

May observe any of the following:

• Scratching, peeling, or cracking of skin around the rim of the ear especially in association with sarcoptic mites.
• Pus or exudate, foul odor, redness and irritation, swelling, or unusual tissue growth in or around ear.
• Pain or discomfort when ears or surrounding area touched.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.

Etiology

Otitis Externa is inflammation of the outer portion or epithelium of the ear.
Some of the causes associated with this may include the presence of otitis media/interna, parasite infestation such as seen with sarcoptic mites, bacterial, fungal, or yeast infections, hypersensitivity or an atopic dermatitis, allergy response, keratinization disorders, or autoimmune disorders (e.g., auricular chondritis in some aging rats). Opportunistic infections where systemic disease is already present may also be another factor.

Histopathological changes may occur when otitis externa is chronic, or when infection is difficult to treat. Some changes that may be seen are swelling of tissue in or around the ear due to sebaceous cysts, abscesses, polyps, and squamous metaplasia or tumor growth, especially if there is a foul odor or drainage.

Therapy should be directed at correcting the underlying cause or there may be a recurrence. A chronic infection or change in the ear may reflect a systemic disease process, or may be caused by an existing infection in the middle ear via a ruptured tympanic membrane.

Figures

Case Histories Showing Otitis Externa

• Fig. 1: (linked from polyp page) Auricular (ear) polyp, a case history and photos of 1 1/2-year-old rat (Lukkas)
• Fig. 2: (linked from squamous cell page) Tumor located in Zymbal’s gland near the base of the ear in male rat (Ramekin)
• Fig. 2: (linked from ectoparasite page) Sarcopetes (type of mite) Mange photos and case history of rat (Sunny)

Diagnostics

Obtain history to determine underlying cause.

Examine both ears for comparison.

Examine for changes in the appearance of the pinna. Cauliflower shaped pinna may indicate auricular chondritis. A brown or black crumbling exudate may indicate mites (notoedres or sarcopetes). A purulent exudate or sweet smell may indicate the presence of bacteria or yeast. Examine canal and structures surrounding the ear for presence of neoplasia (e.g., polyps in canal, Zymbal’s gland tumors at base of ear near jaw).

Otoscopic exam to rule out otitis media.

Obtain skin scrapings for dermatopytes.

Obtain smears to rule out overgrowth of bacteria such as staphylococci, streptococci, and Psuedomonas aeruginosa.

Obtain culture and sensitivity if warranted.

Radiography if warranted.

Treatment

Refer to the Rat Medication Guide, for medication information and dosages.

For mite infestation

May treat with ivermectin orally or topical, or thiabendazole topically.

*Note: If treating for mites be sure to treat the affected rat’s cage mates as well. For additional information on the treatment of mites see article on Ectoparasites in the health section of the Rat Guide.

For Topical Treatment

If exudate is present and tympanic membrane intact, an ear wash such as Epiotic, OtiClens, OtiRinse, or warmed preservative-free normal saline (for a saline solution at home mix 1 teaspoon of salt in 1 pint of warm water) may be used to flush ear.

If an acetic acid is required in the solution the following may be used: Otic Clear, Otocetic, or AloCetic.

*Note: If planning to use an aminoglycoside, it is necessary to cleanse or remove exudate since drugs in this group are inactivated in the presence of pus/exudate.

Be sure to dry ear before applying cream or ointment.

Topical agents are varied, and use may be based on the organism(s) or condition being treated.

Some of those agents the veterinarian may select are topical otic antibiotics or antifungals that may include a steroid such as: Treasaderm (containing neomycin sulfate, thiabendazole, and dexamethasone), or Gentocin Otic (containing gentamicin sulfate, and betamethasone valerate), or topical otics that may require an addition of a systemic or topical steroid such as: Baytril Otic (enrofloxacin/silver sulfadiazine) primarily used for Gram-neg. infection, or Silver sulfadiazine (Silvadene).

*Note: The use of a corticosteroid either topically or systemically can aid in reducing exudate and tissue growth as well as relieve itching. Its use may predispose to yeast infections; however, the benefit in many cases with rats far outweighs the risk. If yeast is present, or of concern, the veterinarian may choose to include a topical agent containing nystatin, thiabendazole, or clotrimazole, or a systemic antifungal medication such as ketoconazole.

In addition, an agent such as Tris-EDTA may be instilled in the ear canal prior to the use of topical otic antibiotics to enhance their activity.

For Systemic Treatment

If tissue appears ulcerated, if exudate contains the presence of bacteria, if the tympanic membrane is ruptured, or an otitis media thought to be a perpetuating cause, administration of systemic antimicrobials is recommended.

See Otitis Media/Interna/Labrynthitis for a listing of recommended antimicrobial agents.

For treatment of polyps or abnormal growths

Surgery may be indicated to debulk growth if feasible.

Nursing Care

• When cleaning ear of debris, or to soak up any drainage, a wick may be fashioned of cotton balls or absorbent towels. Care should be taken if using Q-tips (swabs) in order to prevent abrasions to the tissue in the ear, and the packing of wax or debris against the ear drum.
• Give medications for the length of time prescribed. When administering topical agents: instill medicine, gently hold ear closed, and massage ear canal 30 to 60 seconds to ensure dispersion of medication.
• Maintain clean cage environment.
• Maintain safe environment, particularly if sense of balance is affected.
• Keep food and water within easy access to rat.
• Provide high calorie foods and encourage fluids during illness.
• Contact veterinarian if there are increased signs of infection: redness, swelling, and pain, or if there is weight loss.

Outcome

• Infection/inflammation resolved
• Underlying conditions identified and treated
• Sense of balance maintained
• Itching resolved
• Pain resolved

Prevention

• Treat any respiratory illnesses promptly.
• Treat underlying diseases, as appropriate, to reduce tilting.