Vestibular disease can be a distressing affliction to your pet’s health. Clinical signs may be as mild as a head tilt to severe as inability to stand. You may notice random eye movement (called nystagmus), dragging of the feet, incoordination, circling, or flailing. The video below shows a dog with nystagmus.
These signs may come about very quickly but are seen as a gradual onset as well. Below is a video demonstrating the incoordination of a dog with vestibular disease.
Normal Ear Anatomy
Before one can truly understand vestibular disease, one has to understand the anatomy of the ear and its relation to the vestibular apparatus. Note how different the dog ear is to the human ear. Notice that the dog’s ear canal has a vertical and horizontal portion, making a 90 degree angle in the canal. Past the tympanic membrane (eardrum) sits the middle ear. Encased by bone further in, the inner ear contains all of the neurologic parts of the hearing and vestibular systems. The main balance/hearing nerve (the vestibule-cochlear nerve) has its two main branches travel in this area. This location is also home to numerous major nerves and blood vessels.
Normal Vestibular Function
In addition to knowledge of anatomy, a basic understanding of how these structures work will give
understanding into disease in this area. Balance in animals, and humans, comes from three neurologic pathways. When the head and body move, fluid in the vestibular apparatus moves with it. Hair cells located in the middle ear will fire off neurologic signals in response to this movement. By reading these signals, the brain knows how the head and body are oriented. Gravity receptors in the skin combined with the visual system make up the remaining balance system. With the information gained from all of these systems, the brain is able to orient the body properly. If there is disease with these systems, vestibular disease can manifest.
Peripheral and Central Vestibular Disease
Vestibular disease in the dog is divided into two main categories: peripheral and central. Peripheral diseases make up all disorders arising from everything not included in brain, brainstem, and spinal cord (typically referred to as the central nervous system, or CNS). Central vestibular disease consists of all CNS related syndromes. As a general rule, central vestibular disease carries a worse prognosis than peripheral.