What is it?
The vestibular system is part of the body’s neurological system and is divided into two parts: the peripheral and the central vestibular system. The peripheral system includes receptors in the inner ear and a nerve (cranial nerve VIII) which carries information to the brainstem. The central system includes structures in the brain. Together, these are responsible for an animal’s sense of balance, orientation, and motion. Abnormalities of the vestibular system can result in a head tilt, circling, stumbling, rolling, contraction of the neck muscles (torticollis), incoordination, and involuntary rhythmic movement of the eyes (nystagmus).
What causes vestibular disease?
A bacterial infection of the inner or middle ear is the most common cause of vestibular disease in pet rabbits. The primary agent in these cases is Pasteurella multocida. However, other bacteria including Staphylococcus, Bordatella, E. coli, and Pseudomonas have been isolated. A protozoal infection with Encephalitozoon cuniculi is another common cause of this disease. A severe otitis externa (external ear infection), trauma, cancer, parasite migration (including the raccoon roundworm, Baylisascaris procyonis), toxins (especially lead or zinc), heat stroke, and vascular events (stroke) are less common causes of these signs.
Diagnosis
Your veterinarian will perform a thorough physical examination, including a neurological exam and examination of the eyes and ears. If any discharge is present in the ear, cytology and a culture may be performed.
Routine laboratory tests may be performed, but are often normal. Radiographs (x-rays) of the skull may alert your veterinarian to chronic infection, trauma, dental disease, or cancer in the area of the inner ear. These usually need to be performed under sedation. Serological blood tests for Pasteurella multocida and Encephalitozoon cuniculi can be performed. A positive test only indicates exposure to the organism, though a negative test rules out the organism as a possible cause. If the history indicates a possible exposure to heavy metals, lead and zinc levels should be submitted. Rarely, an analysis of the cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) and/or a CT scan may be recommended.
Often, the cause of the vestibular disease cannot be established and a tentative diagnosis is based on response to therapy. Rabbits with a bacterial infection will often improve with antibiotics and supportive care, while those with other causes are usually unresponsive or worsen despite therapy.
Treatment
If a specific cause for the vestibular disease is identified, that disease is treated accordingly. If a specific cause cannot be established, treatment is supportive and aimed at making your pet as comfortable as possible. Since stimulation of any kind can worsen the clinical signs of vestibular disease, it is important to keep your pet as quiet as possible. Confinement to a small, dark, quiet cage is best. Make sure to remove any objects that could cause harm to your pet if he or she rolls or falls over and avoid any access to stairs. Try to limit your rabbit’s exposure to loud noises and bright lights. If your rabbit is unable to move, he or she should be turned every 6-8 hours or propped up sternally to prevent congestion in the lungs. Nursing care is necessary to prevent urine scalding and dermatitis. If your pet has difficulty eating on its own, you may need to offer food by hand or syringe feed several times a day. Hospitalization may be necessary.
Antibiotic therapy should be provided for a minimum of 2-4 weeks. If a culture was obtained, the antibiotic should be selected based upon those results. Otherwise, enrofloxacin, ciprofloxacin, or TMS can be tried. Metoclopramide (Reglan) is often prescribed for rabbits on antibiotics to help maintain a normal appetite. Many animals become nauseous secondary to vestibular disease, and your veterinarian may prescribe an anti-vomiting or motion sickness medication such as meclizine. Unfortunately, there is no treatment for E. cuniculi. Once encysted in the brain, anti-protozoal therapies appear to be ineffective. Alternative therapies such as chiropractic and acupuncture treatments have been helpful in some cases.
Content prepared by St. Francis Animal Hospital, 1227 Larpenteur Ave. West, Roseville MN. 55113