How an ear infection causes neurologic signs

More about Ethel… she’s just such a special dog so I can’t stop bringing her up! I wanted to explain why she was showing signs of facial paralysis and head tilt from an ear infection.

So, the ear is split into 3 different parts: the external, middle, and inner ear (see image). Typically, if your pet starts shaking his/her head a lot, itching ears more than normal, or has different ear discharge they will be diagnosed with a outer ear infection (otitis externa). As long as the ear drum (tympanic membrane) is intact, your vet will typically treat with an ear cleaner and drops. An external ear infection, will not cause a head tilt or a head tilt.

The inner ear has super important structures that are part of our vestibular system. The vestibular system helps maintain balance and our normal orientation relative to gravity. It also stabilizes the eyes during head movement to maintain steady vision. The facial nerve (cranial nerve 7) is also located near the middle/inner ear. The facial nerve give the the muscles of the face, some of the glands in our eyes and mouth, and the front of our tongue function.

Infection of the inner ear is called otitis interna and middle ear is otitis media. Otitis media and interna are most commonly caused by an external ear that has gone untreated. The bacteria/yeast spread to infect deeper structures of the ear. Other causes of inner/middle ear issues can nclude cancer, nasopharyngeal polyps, trauma, development abnormalities, ear toxicity (ototoxicity), and/or foreign objects.

An infection of the middle and inner ear can cause damage to the vestibular system and the facial nerve. AND THIS IS WHY ALL EAR INFECTIONS SHOULD NOT BE LEFT UNTREATED!

A pet with an inner ear infection will show vestibular signs like a head tilt and walking in circles/falling towards the ear with the infection. They will also have weird eye movement (nystagmus) or positioning (strabismus). Usually, only one ear is infected but if both are then the animal will not show the above signs. They will usually also have facial nerve paralysis (droopy lip, visible third eyelid, inability to blink, etc.) on the same side of the face as the infected ear.

There is a potential that the infection can extend even further into the head and cause brain / central nervous system issues too.

These infections are difficult to treat because the structures of the inner/middle ear are super sensitive so we cannot treat with ear drops. Instead, we have to treat the infection with systemic/oral medication. It takes a lot longer for oral medication to penetrate into the ear to kill the infection than it would if we could treat with ear drops. If suspected, we take a sample of the infected ear to send to a lab to make sure we are using the right antibiotics to treat.

Once diagnosed, the pet will need to be sedated and the ear will be flushed/cleaned with sterile saline.

Along with antibiotics/ antifungals, he/she will need a anti-inflammatories or steroids to reduce the inflammation/itch, anti nausea meds for the dizziness, and pain medication.

Animals on treatment, should be rechecked every 2 weeks to evaluate if the infection is getting better and if the ear drum is rupture/ healing. Typically, treatment last 6-8 weeks. Once the infection is cured, there is a chance that some neurologic issues may persist post treatment.

Ethel has come a long way since her initial diagnosis! But, I am suspicious, she may have persistent facial nerve paralysis forever.

(Image is taken from Practical Otic Anatomy and Physiology of the Dog/Cat)

#SGAS #vetgirl #girlvet

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