EQUUS CONSULTANTS

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Q:For about a year, I had been having problems with blurred vision and a slight balance issue. My doctor diagnosed it as an inner ear problem. The issue turned out to be water: I had been using a spray nozzle to rinse my hair, and I would occasionally get water in my ears. Once I learned this, I took care to keep water out of my ear canals and my balance and eye problems both cleared up.

My question is, can horses have this problem? I am careful not to get water in my horses’ ears while I bathe them, but I know a lot of people spray their horses’ faces more indiscriminately. Is it possible that water in a horse’s inner ear might be misdiagnosed as a mild case of wobbles or EPM? Ann Barosh Huntsville, Texas

A:It would be difficult to get a significant amount of water into a horse’s ear canal as you were bathing him. In contrast to the human ear canal, which is short and straight, a horse’s ear canal is long and runs inward at an angle. Plus, most horses have a fair amount of hair in their ears that protects the opening to the canal, which is quite small.

That said, horses certainly can have middle ear and vestibular system issues that result in balance problems. The vestibular system is the sensory mechanism in the inner ear that detects movement of the head and helps to control balance.

Vestibular disease in the horse may result from a number of infectious, traumatic and other conditions. Head trauma and temporohyoid osteoarthropathy (THO) are two of the most

common. THO is a chronic, bony overgrowth on the stylohyoid bone where it connects with the base of the skull at the temporohyoid joint, near the middle ear. (The stylohyoid bones are part of the hyoid apparatus, a set of bones that form a “swing” shape below the back of the skull and support the larynx and the base of the tongue.) The cause of the bony overgrowth is not completely understood but it could be due to trauma, osteoarthritis or infection spreading from the nearby middle ear or guttural pouches.

The bony overgrowth causes joint fusion (ankylosis) of the temporohyoid joint. This decreases the range of movement of the joint so actions such as swallowing or moving the neck or head can cause fractures at the site of the fusion. The resulting swelling and inflammation put pressure on nearby structures and can lead to neurological and other signs, including discharge---blood, pus or spinal fluid---from the ear, difficulty swallowing (dysphagia), a head tilt, involuntary movement of the eyeballs (nystagmus), misalignment of the eyeball from its normal position (strabismus), circling, incoordination (ataxia) and facial nerve paralysis.

THO is usually diagnosed by an endoscopic examination of the guttural pouches---the bony overgrowths would be clearly visible. Other diagnostic options include skull radiographs and computed tomography.

The guttural pouches are unique to a small number of animal species, including the horse. There are two guttural pouches---sacs of air that expand from the eustachian tubes---one beneath each ear. In a mature horse, each guttural pouch cavity can hold as much as a coffee mug. The guttural pouches are lined with a very thin membrane and beneath that membrane are some critical structures, such as major arteries to the head and some of the most important nerves in the body. Most of these nerves are cranial nerves, so when they are damaged, the resulting clinical signs relate to functions of the head.

Other potential causes of vestibular disease in horses include equine0 protozoal myeloencephalitis (EPM),

Horses certainly can have middle ear and vestibular system issues that result in balance problems.

abnormal tissue growths (neoplasia), brain abscesses, West0 Nile encephalitis, eastern0 equine encephalomyelitis (EEE) and parasitic migration.

So while horses do have diseases that affect their balance, due to differences in their anatomy it would be extremely unlikely for balance issues to be caused by getting water into their external ear canal. Sandra Sargent, DVM, DACVD Pittsburgh Veterinary Dermatology Pittsburgh, Pennsylvania