Infections of the middle and inner ear can be recognized by signs of labyrinthitis. The labyrinth is a complex organ composed of three semicircular canals: the utricle, saccule, and cochlea. The labyrinth is like a gyroscope. Its purpose is to synchronize eye movements and maintain posture, balance, and coordination. A horse with labyrinthitis will often assume an abnormal posture with a head tilt toward the affected side. Dizziness, incoordination, and loss of balance are evident in the staggering gait, turning and circling toward the affected side, and tendency to lean against walls and fences for support. The horse may exhibit rapid jerking movements of the eyballs, a condition called nystagmus.
The usual cause of inflammation of the labyrinth is a bacterial infection of the middle and inner ear. Encephalitis, meningitis, and ryegrass staggers can produce signs of labyrinthitis. These signs can also occur with brain tumors, antibiotic-induced damage to the auditory nerves, antifreeze poisoning, and a condition called idiopathic vestibular syndrome. This syndrome is thought to be caused by a virus.
The treatment is directed at the primary disease. Bacterial infection require high-dose antibiotic therapy. The horse should be confined to a quiet, well-bedded stall. Horses that recover from labyrinthitis may exhibit head-bobbing or a coarse tremor of the head, evident during eating or drinking. They are prone to episodes of imbalance and may pose a hazard when used for sport or pleasure.