Although they don't tend to garner as much attention as infectious neurologic diseases, vestibular diseases (those that pertain to the balance mechanisms) are common and important causes of neurologic problems in horses. At the 2013 Western Veterinary Conference, held Feb. 17-21, Laurie Beard, DVM, MS, Dipl. ACVIM, associate clinical professor at Kansas State University's College of Veterinary Medicine, described the two most common vestibular diseases in horses: temporohyoid osteoarthropathy (THO) and skull fractures.
Beard used case studies to present a review of the clinical signs, diagnostic methods, and treatment options for the two disorders. She explained that some clinical signs are common among the different vestibular disease, including:
- Head tilting;
- Nystagmus (involuntary movement of the eyeballs);
- Ataxia (incoordination);
- Strabismus (misalignment of the eyeball from its normal position); and
- Facial nerve paralysis.
Beard explained that THO is a chronic, bony growth on the stylohyoid bone in the temporohyoid joint associated with the skull and located near the middle ear and guttural pouch, which results in ankylosis (joint fusion). The disorder's cause is unknown.
According to Beard, clinical signs of THO include:
- Acute onset neurologic dysfunction;
- Unilateral (one sided) facial and/or vestibular nerve dysfunction or paralysis;
- Discharge—blood, purulent exudates, or spinal fluid—from the ear;
- Dysphagia (difficulty swallowing); and
- Head tossing, ear rubbing, and bridling problems.
THO diagnosis generally includes endoscopic examination of the guttural pouches, Beard said, as the bony proliferation is often easily visible upon endoscopic exam. Other diagnostic options include skull radiographs and computed tomography, he said.
Beard said most horses respond well to conservative treatment, including broad spectrum antibiotics and non-steroidal anti-inflammatory drugs.
"The goals of conservative treatment are to reduce inflammation and potentially treat any infectious process (in some cases a middle ear infection is believed to be the inciting cause)," Beard said. Treatment usually lasts for four to six weeks, followed by a six- to 12-month for nerve healing period, she explained. Conservative treatment, however, will not eliminate the bony proliferation, she said.
Some cases require more aggressive surgical treatment. Beard said that a ceratohyoidectomy—complete removal of the entire ceratohyoid—has recently been reported successful. She said that good surgical candidates for ceratohyoidectomy have no neurologic dysfunction, but have problems eating.
"It's unclear if surgery is more effective than conservative management in all cases," she said.
Skull fractures generally occur when horses flip over backwards, Beard said. Common fracture locations include the basisphenoid, basioccipital, and temporal bones, she noted.
Beard said that common clinical signs of skull fractures include:
- Loss of consciousness for minutes to hours;
- Vestibular dysfunction;
- Facial nerve paralysis;
- Hemorrhage from the ears or nostrils;
- Ataxia; and
- Spinal fluid leaking from the ears.
Beard said that in many cases a skull fracture can be diagnosed because the horse's owner or handler saw the accident occur. However if the veterinarian has no history about the injury, he or she can use endoscopy (to look for blood in the pharynx, guttural pouches, or upper airway walls) or computed tomography (which Beard noted requires general anesthesia). Radiography can be difficult to evaluate, she cautioned, because these fractures frequently have minimal displacement.
Skull fracture treatments include anti-inflammatories (both steroidal and non-steriodal), diazepam or phenobarbital to treat seizures, and broad-spectrum antibiotics if fractures have broken the skin. Beard said veterinarians might administer mannitol and/or hypertonic saline to help reduce associated central nervous system edema; however, this should not be used on horses with active hemorrhaging into the brain. "These fractures are usually not significantly displaced and allowed to heal naturally," Beard said.
Beard said that in most cases, the prognoses for both THO and skull fractures are good, although both disorders typically require significant time to heal. She also noted that recumbency (the inability to stand) lasting more than four hours is associated with a poor prognosis.
Skull fractures and THO are the most common equine vestibular diseases, Beard concluded. In most cases, both can be treated and have a good prognosis.
About the Author
Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.