Temporohyoid osteoarthropathy

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Temporohyoid Osteoarthropathy

Otitis Media-interna

Temporohyoid osteoarthropathy (THO), also known as otitis media-interna, is a progressive disease of the middle ear and temporohyoid joint that affects the stylohyoid and petrous temporal bones. THO affects all ages, breeds and gender of horses, worldwide.

THO is thought to be caused by an inner or a middle ear infection of hematogenous orgin that spreads to the associated bones, causing them to thicken and the temporohyoid joint to fuse. Other possibilities for its onset are from guttural pouch infection, nonseptic osteoarthritis, or from extension of otitis media/externa. Once the temporohyoid joint fuses and the associated bones thicken, the resulting forces produced during swallowing, teeth floating, oral or dental examinations, combined head and neck movements, or during vocalizing can potentially result in fractures of the petrous part of the temporal bone, causing dysfunction of the facial nerve (CN VII) and vestibulocochlear nerve (CN VIII).

Initial, early clinical signs of THO in horses include frequent ear rubbing, refusal to take the bit, head tossing, resistance to digital pressure around the base of the ears or on the basihyoid bone, refusing the position the head properly when saddled, and other nonspecific behavioral changes. Most horses also develop signs of facial nerve damage, such as inability to close the eyes, paresis or paralysis of the ear on the affected side, decreased tear production, and deviation of the upper lip away from the affected side. Horses that are unable to close their eyes and experience decreased tear production often develop corneal ulcers, keratitis, and keratoconjunctivitis.


Head tossing
Ear rubbing
Refusal to take bit
Head tilt
Difficulty handling head
One ear drooping
Leaning against the wall
Asymmetric ataxia
Decreased tear production
Inability to close eyes
Upper lip abnormality
Signs made worse when blindfolded
Secondary corneal ulceration


  • History
  • Clinical signs
  • Physical exam
  • Radiographs of the skull
  • Endoscopy of the guttural pouch
  • Computed tomography or MRI can demonstrate bony and soft tissue changes in the middle and inner ear.



Broad spectrum antibioticsAs needed for infection
NSAIDsHelp to reduce pain and inflammation
Dimethyl sulfoxide
Supplemental tears
SurgeryCeratohyoidectomy (89% of horses showed substantial improvements over the first 6 months following surgery, with continued improvement for the reminder of the year.



Has a varied prognosis, if treatment is delayed neurologic signs are more likely to persist.

Scientific Research

General Overviews

Clinical Trials

Age Range

The disease is most common in middle age horses but can affect horses of any age.

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