The most common cause of peripheral vestibular disease in older subjects is Idiopathic Benign Vestibular Disease (IBVD). This condition can occur in dogs and cats of any age but the average age of onset in dogs is 12.5 years; therefore, it is also often referred to as Idiopathic Geriatric Vestibular Syndrome, to emphasize the fact that it occurs more frequently in older patients.
The onset of vestibular signs is acute and the course is progressive during the 24-48 hours after onset. This is followed by stabilization and then an improvement, of variable degree, that occurs after a few days or weeks. Occasionally, a slight rotation of the head may persist (Fig. 1) even after the event. The degree of manifest ataxia is generally moderate (the animal is capable of maintaining a standing position, but often stumbles and falls), or severe (unable to maintain the standing position or walk without support). Rolling and circling are not commonly manifested, and in most cases nystagmus has a rotational component. Facial paralysis and Horner's syndrome do not occur in this disease. At the onset of symptoms approximately 40% of dogs manifest vomiting. The vestibular symptoms are sometimes so severe that the neurological examination becomes extremely difficult, especially in cats.
It is important to distinguish between this benign idiopathic disorder, which resolves spontaneously without treatment, and otitis media-interna, which requires a vigorous antibiotic treatment and is likely to show recurrent or persistent symptoms.
Animals with unilateral vestibular signs with acute onset and without a history of trauma are diagnosed as suffering from IBVD if there are no physical abnormalities in the tympanic membrane and radiographic changes in the tympanic bullae and in the petrous portion of the temporal bone. In the past this has been the standard protocol for the diagnosis of IBVD. Today, due to a more widespread use of advanced imaging tools, such as Computed Tomography and Magnetic Resonance, certain conditions diagnosed as idiopathic vestibular syndromes may actually have a different explanation.
Due to the advanced age and the dramatic nature and acuteness of the symptoms, this syndrome was once mistakenly called “stroke”, when in fact a stroke involves a haemorrhage in the brain-stem. In the past, many of these animals were euthanized on the spot because it was thought they had a serious and irreversible disease of the central nervous system.
The pathogenetic mechanism underlying IBVD in dogs is unknown. In some cases, the histological exam shows no alteration in the central nervous system, at the level of the vestibular nerve, the vestibular ganglion and the vestibular receptors of the membranous labyrinth. Possible causes include neuritis of the vestibular portion of the eighth cranial nerve or abnormalities in the dynamics of the endolymphatic flow inside the labyrinth. In several dogs, relapses were observed always on the same side or even on the opposite side, though much more rarely.
DIAGNOSIS
The term 'idiopathic' refers to a disease with characteristic symptoms for which an aetiological diagnosis has not been definitively assigned. Therefore, as with all other conditions considered idiopathic, a diagnosis is reached by excluding all other possible causes that might produce the same symptoms.
The diagnostic protocol includes the performance of an otoscopic examination, an evaluation of the haemato-biochemical profile and advanced imaging studies, particularly MRI. In order to be able to confirm a diagnosis of idiopathic vestibular syndrome, the collateral exams must invariably be within the norm.
TREATMENT
From the therapeutic point of view, there is no specific treatment and the use of corticosteroids has not led to a faster or better recovery in affected animals. Recovery is consequently spontaneous and does not require specific therapeutic interventions.
Suggested readings
- Rossmeisl J.H., (2010): Vestibular Disease in Dogs and Cats. Veterinary Clinics of North America: Small Animal Practice, 40(1):81-100.
- De Lahunta A., (2008): Vestibular system – special proprioception. Veterinary neuroanatomy and clinical neurology. Philadelphia: W.B. Saunders.
- Dewey C.W., (2009): A practical guide to Canine and Feline Neurology. Blackwell Publishing.
- Thomas W.B., (2000): Vestibular disfunction. Veterinary Clinics of North America: Small Animal Practice, 30: 227-249.
- Le Couter R.A., (2006): Vestibular diseases of cats and dogs. In: NAVC Proceedings 2006, North America Veterinary Conference (Eds). Publisher: NAVC (www.tnavc.org). Internet Publisher: International Veterinary Information Service, Ithaca NY (www.ivis.org).
- Platt SR, Olby NJ., (2004): BSAVA Manual of Canine and Feline Neurology. BSVA 3rd edition.