Otitis Media and Interna in Horses

Inflammation of the middle ear structures (otitis media) is usually due to extension of infection from the external ear canal (through the eardrum) or from the throat (through the auditory tube). Spread of infection by means of blood to these areas or from the inner ear is possible but rare. Inflammation of the middle ear may lead to inflammation of the inner ear structures (otitis interna). This can, in turn, lead to loss of balance and deafness.

One or both ears may be affected. The signs of otitis media include head shaking and tilting or rotating the head toward the affected ear. When otitis media spreads to (or from) the external ear, signs of otitis externa are seen. Because the facial and sympathetic nerves travel through the middle ear, facial nerve paralysis or Horner syndrome (constriction of the pupil of the eye, drooping of the eyelid, sinking of the eyeball into the orbital cavity, and protrusion of the third eyelid) may occur on the same side as the affected ear. If otitis interna occurs at the same time, head tilt toward the affected side will be more obvious. Additionally, an animal with inflammation of the inner ear may have an overall lack of coordination. An involuntary rhythmic movement of the eyes from side to side (called nystagmus) may also be seen with inflammation of the inner ear. If the inflammation spreads to the brain, neurologic signs can be seen.

In horses, severe inflammation of the inner or middle ear can lead to bony overgrowth and fracture of the tympanohyoid joint (a joint between the skull and the bones found within the throat). This fracture can extend to the skull, leading to infection or bleeding under the skull, which can be fatal.

The diagnosis of otitis media and interna is based on the horse's history and signs. Veterinarians may suspect the condition in horses that have signs and a history of bottle feeding or ingesting contaminated milk in newborn foals; previous or current respiratory disease; longterm ear infections; or a foreign object in the ear. The condition is confirmed by visualizing the diseased ear drum with an otoscope. Because it is difficult to see the ear drum in horses, specialized equipment (a video otoscope, endoscope, x-rays, computed tomography, or magnetic resonance imaging) may be necessary to confirm the diagnosis.

The treatment of otitis media and interna is most successful when started right away. Longterm cases may not respond to treatment or may recur after treatment is stopped. Treatment involves eliminating any bacterial or parasitic infections, reducing inflammation and pain, and managing complications. Your veterinarian will recommend an appropriate treatment plan.