By Dr. Gail Mason, DVM, MA, DACVIM
The vestibular system is comprised of neurological components responsible for perceiving one’s body orientation relative to Earth. In simplest form, it is the electronic system which maintains balance, informs your brain, eyes, and extremities how they should move according to your position in space. The vestibular system has central components located within the brain, as well as peripheral components which are in the inner and middle ear canal.
Vestibular disease is defined as sudden non-progressive disturbances of balance. It is most common in older dogs and more common in medium to large breeds. Most dogs present with sudden loss of balance, disorientation, head tilt, and irregular rapid eye movements called nystagmus. Many dogs will be reluctant or unable to stand (referred to as “ataxia”) and will lean or fall to a preferred side. Nausea, drooling, and vomiting are not uncommon. The symptoms are so dramatic and sudden that many owners believe that their pet has had a stroke. The term “stroke”, however, refers to a vascular accident, which is an extremely uncommon event in canines.
What Causes Vestibular Disease?
By far, the most common type of these symptoms in dogs is referred to as “old dog vestibular syndrome,” or ODVS when the exact cause is idiopathic or “unknown”. It may result from abnormal flow of fluid within the semicircular canals of the inner ear. The symptoms can happen extremely rapidly, even over several minutes, and can cause severe incapacitation. However, this syndrome tends to be self-resolving with improvement beginning within 72 hours. Most affected dogs will be clinically normal within 1 to 2 weeks after onset. Occasionally, the head tilt will persist but does not negatively impact the animal.
Inner & Middle Ear Inflammation or Infection
As mentioned, the vestibular apparatus also involves structures within the middle and inner ear. Damage to these structures by inflammation, infection, or trauma can also cause signs of vestibular disease. Less commonly, certain systemic drugs or topically applied ear medications can cause these symptoms. In the latter case, the risk is higher in patients who have ruptured eardrums which allows easy access of medications to the middle and inner ear structures.
Hypertension
In general, hypertension as a primary disease would be a very uncommon cause of vestibular signs in dogs. There is a rare tumor of the adrenal gland, called a pheochromocytoma, which can produce extremely high systemic blood pressures to the point where a vascular accident occurs within the vestibular system.
How Is Vestibular Syndrome Diagnosed?
The first step in making an accurate diagnosis of ODVS is to give your veterinarian an accurate medical history, including past and present health issues. Typical history will include a sudden onset of imbalance, disorientation, a head tilt, and irregular eye movements. Many patients are unable to stand and will fall to one side. While this is alarming to watch, remember that in most cases it is benign and reversible.
The next step in the process is a thorough physical examination. The veterinarian will attempt to determine if there has been any trauma or any history of ear infections (especially those that have been chronic). The exam will often include a thorough inspection of the ear canals.
Lastly, a neurologic examination helps determine the cause of the vestibular signs. The veterinarian assesses the overall mental status of the patient, the direction of the rapid eye movements (usually horizontal or rotary, with the fast movement away from the most affected side), the direction of the head tilt (usually towards the more severely affected side), and whether there appears to be deficits of any other neurologic functions. In most cases, the cause can be sourced to either “central” (within the brain) or “peripheral” (nerves near the inner/middle ear apparatus). At this point, a preliminary diagnosis of ODVS may be given at this point. If this diagnosis is correct, then the patient should be given “tincture of time” to recover. If your veterinarian has concerns that the cause may be central in origin or from a more concerning cause, then additional diagnostics may be requested.
A database consisting of a CBC or blood count, plus a chemistry panel to determine organ function can be helpful in eliminating other serious illnesses. In certain patients, blood pressure measurements and/ or radiographs may be indicated. If the dog’s symptoms do not improve, and /or worsen, or become recurrent, then more sophisticated diagnostic Imaging such as a CT scan or MRI would be appropriate.
Treatment
For dogs that have vestibular symptoms secondary to disease of the ear canal, the recommended approach may include examination of the ear canal under anesthesia, X-rays of the skull and ear (bulla), as well as culture and biopsy of the affected area. Deep infections of the inner ear can be difficult to eradicate and may require a surgical procedure called a bulla osteotomy for drainage.
For dogs that are severely affected or that may have additional health issues, temporary hospitalization and supportive care may be helpful. This would generally be in the form of fluid therapy to maintain hydration and anti-nausea drugs to reduce vomiting and dizziness. Fortunately for you and your best canine friend, most vestibular patients will recover fully on their own.
Dr. Gail Mason, DVM, MA, DACVIM
Staff Internist, Portland Veterinary Emergency & Specialty Care