Vestibular Disease

Chapter 104 Vestibular Disease






NEUROANATOMY OF THE VESTIBULAR SYSTEM


The vestibular system can be divided into peripheral components located in the inner ear and central nervous system (CNS) components. Three major CNS areas receive projections from the peripheral sensory receptors of the vestibular system: the cerebral cortex, the spinal cord, and the cerebellum. The projection to the cerebral cortex incorporates extensions to the extraocular muscles.



Nerve Pathways to the Extraocular Muscles


Two neurons make up the pathway responsible for the sensory input of the head to the cerebral cortex (Figure 104-1).








CLINICAL SIGNS


Unilateral vestibular disease produces asymmetric signs, often on or toward the side of the disease. The most common clinical signs of vestibular disease are head tilt, nystagmus, and ataxia; these may be single entities or a combination of signs.2 The primary aim of the neurologic examination is to determine if these vestibular signs are due to a peripheral vestibular system (inner ear) disease or a central vestibular system (brain stem and cerebellum, or both) disease. Localization of the disease determines the most appropriate diagnostic tests, the differential diagnoses, and the prognosis.


The essential determination of whether these signs are due to a peripheral or central disease may be possible by the identification of associated neurologic signs that are present only with central disease.2 Signs of central vestibular syndrome suggest damage to the brain stem and are not present in patients with inner ear disease unless there has been extension of the inner ear disease into the brain stem, such as can be seen with otitis media, otitis interna, and neoplasia.3



Specific Signs of Vestibular Dysfunction


Signs of vestibular dysfunction are outlined in Table 104-1.


Table 104-1 Neurologic Examination Findings in Animals With Peripheral and Central Vestibular Dysfunction







































Clinical Signs Peripheral Vestibular Disease Central Vestibular Disease
Head tilt Toward the lesion Toward the lesion, or away from the lesion with paradoxical disease
Spontaneous nystagmus Horizontal or rotatory with the fast phase away from the side of the lesion
Rarely positional
Horizontal, rotatory, vertical and or positional with the fast phase toward or away from the lesion
Paresis and proprioceptive deficits None Commonly ipsilateral to the lesion
Mentation Normal to disoriented Depressed, stuporous, obtunded, or comatose
Cranial nerve deficits Ipsilateral CN VII deficit Ipsilateral CN V, VII, IX, X, and XII
Horner’s syndrome Common ipsilateral to the lesion Uncommon
Head tremors None Can occur with concurrent cerebellar dysfunction
Circling Infrequent but can be seen toward the side of the lesion Usually toward the side of the lesion

CN, Cranial nerve.


Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Vestibular Disease
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