The vestibular system, in conjunction with other systems, maintains equilibrium and balance. Anatomically, it can be separated into peripheral components, which reside within the inner ear and petrous temporal bone, and central components, which are located primarily within the caudal portion of the brainstem but interact with structures in the cerebellum, midbrain, and cranial cervical portion of the spinal cord. Exclusive of seizures, vestibular dysfunction is one of the most common indications for advanced imaging (MRI or CT) of the head in small animal neurology patients.
Diagnosis of vestibular disease and, in large part, determination of whether to pursue advanced imaging and the type of advanced imaging to pursue are highly dependent on findings of the neurologic examination. Other than neurologic examination, no clinical tests exist that can establish the presence of vestibular dysfunction. In addition, a definitive diagnosis of vestibular disease associated with dysfunction of central components often requires more expensive and aggressive diagnostic testing and treatment.1 Therefore, it is important that neurologic examination findings indicative of vestibular disease, as well as localization of the dysfunction to central or peripheral structures, be highly reliable and strongly predictive of eventual definitive diagnosis.
Key neurologic examination findings generally agreed upon as indicative of vestibular dysfunction include head tilt; abnormal nystagmus; vestibular ataxia characterized by leaning, falling, or rolling to 1 side, with or without neck and trunk deviation with concavity to the same side; and vestibular strabismus, defined as a unilateral ventral or ventrolateral strabismus induced on extension of the head and neck.1–6 Other lesion locations, specifically the thalamus, are also reportedly associated with many of these signs,7 although the relative frequency of these signs in the context of isolated thalamic lesions of different etiologies is not well understood. Also, little is known about the frequency of occurrence of individual vestibular signs as related to the identification of lesions within vestibular structures.
Two studies3,8 have been conducted to investigate, at least tangentially, the relationship between interpretation of neurologic examination findings and eventual localization and etiologic diagnosis of vestibular disease in dogs. Neither of these studies included a comparison group of dogs without vestibular disease, and without such a group, one cannot determine which test findings (in this situation, interpretation of examination and MRI results) have value in the diagnosis of vestibular disease.
The purpose of the study reported here was to explore the reliability of interpretation of neurologic examination results for the identification and localization of vestibular disease in a large number of dogs. On the basis of previous research,3,8 we expected that there would be excellent agreement between clinical localization of lesions to central vestibular structures and identification of lesions of central vestibular structures on MRI and that there would be fair to good agreement between clinical localization of lesions to peripheral vestibular structures and identification of lesions of peripheral vestibular structures on MRI. Our goal was to determine whether specific features of the clinical examination were reliably associated with the presence and location of MRI-identified lesions affecting the vestibular system in dogs.
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