When presented with a horse demonstrating facial nerve paralysis and/or a head tilt, neurologists say veterinarians should consider temporohyoid osteoarthropathy, a disorder of the hyoid apparatus (voice box) and associated structures. Although it is not the most commonly diagnosed neurologic condition in horses, it’s an important and treatable condition that horse owners and their veterinarians should be aware of, according to Steve Reed, DVM, Dipl. ACVIM, and J. Brett Woodie, DVM, Dipl. ACVS, of Rood & Riddle Equine Hospital in Lexington, Ky.

The hyoid apparatus and larynx are suspended from the skull via the temporohyoid joint, which is located in the temporal region of the horse’s head (the region between the larynx and the base of the ear). Temporohyoid osteoarthropathy is a bony proliferation (growth) of the tympanic bulla, proximal stylohyoid, and petrous temporal bones. The result is fusion of the temporohyoid joint and, in some cases, fracture of the small bones that make up the hyoid apparatus.

“While the actual growth of the bones and loss of movement in the joint can be uncomfortable for affected horses, the bigger problem is that fracture of the bones of the hyoid apparatus can occur, which often damages the nearby facial, vagus, glossopharyngeal, vestibular cochlear, and hypoglossal nerves,” Reed said.

Clinical signs in the early stages of the disease, prior to fracture of the bones of the hyoid apparatus, can include ear rubbing, head shaking and tossing, pain on manipulation of the ears and temporal region, bit avoidance, and a reluctance to eat due to pain while chewing