Otitis Media, Otitis Interna / Labyrinthitis

Definition

Ot=ear + itis=inflammation.
Otitis media=inflammation of the middle ear.
Otitis interna/Labyrinthitis=means inflammation of the inner ear and structures.

Clinical Signs

Head tilted or rotated to the side.
Rubbing the head against floor of cage.
Scratching at the ear.
Poor balance and “circling”.
Foul, or sweet, smelling drainage from ear in more advanced infections.
Facial nerve paralysis, blinking of eye, or enophthalmos (recession of eye) on the side affected.
Clinical signs of an external otitis may also be present.

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

Etiology

Inflammation of the middle and inner ear, known as otitis media and otitis interna, respectively, is often associated with upper or lower respiratory infections, or in some instances may be an extension of an external otitis (inflammation of the outer ear).

Otitis media and interna often develop when bacteria, such as Mycoplasma pulmonis, Streptobacillus moniliformis, or Psuedomonas aeruginosa, and viruses travel from the naso-pharynx through the Eustachian tubes to involve the lining of the ear. As the infection progresses to involve the labyrinth structure of the inner ear, inflammation to the vestibular nerve and swelling of the surrounding tissues results in “torticollis” or a tilting of the head. This tilting is most often directed towards the side of the affected ear. It is sometimes referred to as “Head Tilt” or “Wry Neck” (a neuro-muscular response seen primarily in rabbits).

In most cases, when treated promptly with systemic antibiotics to combat infection, as well as a corticosteroid to reduce the swelling of tissue, the head tilt will disappear in a matter of days. However, it is not unusual in some cases for the head tilt to remain throughout the rat’s life. This permanent “tilt” does not seem to pose a significant problem for rats, as they are able to adjust to it very quickly. Where left untreated, the condition could worsen resulting in the loss of balance for the rat, rolling rather than being able to stand or walk, and the inability to feed or care for itself.

It is important to note that there are other conditions that can result in “head tilt” infections of the ear such as: brain injuries (e.g., strokes), pituitary tumors, or trauma. Any disease process which can cause obstruction or inflammation of the inner ear can lead to head tilt.

A final note, when attempting to resolve otitis media or interna, the underlying cause should be determined and treated if possible.

Figures

Case Histories of Otitis Media, Interna / Labyrinthitis

Fig. 1: Inner ear infection and resulting head tilt in 12-week-old male rat (Widget)
Fig. 2: Photos of head tilt due to a variety of causes in rats (Balu and Ruffio)
Fig. 3: Inner ear infection and resulting head tilt in 7-month-old female rat (Maski)
Fig. 4a: Inner ear infection as a result of ulcerated, abscessed, squamous cell lesion in 26-month-old female rat (Jet). Includes link to cleaning of wound and supplies used.

Diagnostics

Obtain history to determine underlying cause.

Assess rat’s balance. Head will often be tilted towards side of affected ear.

Visualization with otoscope may show discoloration, bulging, or rupture of the tympanic membrane. Fluid or exudate/pus may be present in the tympanic cavity. A foul or sweet smell may indicate the presence of bacteria or yeast.

If possible, obtain exudate for culture and sensitivity.

Treatment

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

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.

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

Be sure to dry ear before applying a 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 such as:
Baytril Otic (enrofloxacin/silver sulfadiazine) primarily used for Gram-neg. infection, or Silver sulfadiazine (Silvadene), that may require an addition of a systemic or topical steroid to the treatment.

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:

Begin long term systemic therapy for 3 to 6 weeks, with broad-spectrum antibiotics such as:

If combination antimicrobial therapy is required, the following may be used:

In addition, systemic corticosteroids such as prednisone may be given. Corticosteroids along with a systemic antibiotic should be started as soon as clinical signs of the illness first begin. Doing so can help to decrease the chance of the head tilt becoming permanent.

*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 of using a corticosteroid, in many cases with rats, far outweighs the risk. If yeast is present, or of concern, the veterinarian may choose to include a topical antifungal agent (already included in some topical medications), or a systemic antifungal medication such as: ketoconazole.

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 (cotton 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 head tilt is severe.
Keep food and water within easy access to rat.
Provide high calorie foods (e.g., avocado), or food supplements such as Nutri-Cal Paste, canned Ensure, soy or soy formula, along with a multi-vitamin and mineral supplement (can be found in pet store) if weight loss or food intake is poor.
Contact veterinarian if infection worsens or does not resolve, or if there is decreased appetite and weight loss.

Outcome

Infection and inflammation resolved
Underlying conditions determined and treated
Head tilt is minimized

Prevention

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