Central Vestibular Disease
Any signs of brain stem disease in association with vestibular signs indicate that central involvement is present. The most
frequent differentiating feature is a deficit in postural reactions, as central vestibular lesions most often result in paresis
or loss of conscious proprioception. Alterations in mental status, or deficits in Vth or VIIth cranial nerves, also may be
indicative of central disease. Nystagmus may be a key to differentiating central from peripheral disease. Nystagmus occurs
in most central vestibular syndromes, and appears to be a permanent deficit. It is a positional nystagmus; therefore it may
be present in some head positions (with respect to gravity), but not in others. Also the nystagmus may vary in direction with
change in head position. Vertical nystagmus in any head position is most consistent with central vestibular disease.
Paradoxical Central Vestibular Syndrome
Unilateral lesions of the peripheral vestibular system produce a head tilt towards the side of the lesion. With few exceptions,
the same occurs with lesions of the central components of the vestibular system. Exceptions to this rule are therefore termed
"paradoxical". Some unilateral lesions of the central vestibular pathways, especially unilateral involvement of the flocculonodular
lobe of the cerebellum or the supramedullary part of the caudal cerebellar peduncle, produce a head tilt and ataxia directed
toward the side opposite to the lesion, and a nystagmus with the fast component towards the side of the lesion. Such lesions
usually are space-occupying lesions. Usually these lesions will produce postural reaction deficits or additional cranial nerve
abnormalities on the affected side, which aid in determining on which side a lesion is located.
Bilateral Vestibular Disease
Bilateral peripheral vestibular disease with complete loss of function is characterized by symmetrical ataxia and loss of
balance of either side, with strength preserved. Postural asymmetry is not present. A characteristic "side-to-side" head movement
often accompanies these signs. Abnormal nystagmus is not observed, and with bilateral destruction of the receptor organs,
normal vestibular nystagmus cannot be elicited by head movement or caloric testing.
Diseases Causing Peripheral Vestibular Dysfunction
Anomalous
Congenital vestibular disease is reported in both purebred dogs and cats (GSD, Dobermann, English Cocker, Siamese and Burmese).
Signs are usually unilateral (bilateral in Beagle and Akita). Onset is usually from birth to 3 months of age. Clinical signs
include head tilt, ataxia, usually no nystagmus, ± deafness. Prognosis can be favorable with some animals improving with time
due to compensation.
Metabolic
Hypothyroidism has been associated with polyneuropathy involving CN VII and VIII in adult dogs. Usually presents as unilateral
disease and often progresses to bilateral involvement. Diagnosis is based on physical and neurological examination, thyroid
panel and therapeutic trials (although no proven benefit of supplementation has been demonstrated). This presentation has
also been associated with pituitary chromophobe adenomas. Prognosis is can be favorable with some animals improving with time,
however residual deficits of CN VII are common. Hypoxia may affect the receptor organs.
Neoplasia
Neurofibroma/acoustic neuroma of CN VIII may occur. Usually unilateral signs, often involving CN VII. May affect central structures
with time/growth. Neoplasia involving the petrous temporal bone; osteosarcoma, fibrosarcoma, chondrosarcoma, squamous cell
carcinoma.
Infectious/Inflammatory
1. Otitis-media and otitis-interna: The most common cause of peripheral vestibular disease. Vestibular signs occur when the
middle ear inflammation/infection directly or indirectly affects the function of the membranous labyrinth. Most cases are
due to extension from the external ear, but this is not always the case.
A.
Clinical signs
• Varying degrees of unilateral vestibular disease.
• Acute or chronic onset.
• ± Facial nerve dysfunction
• ± Horner's syndrome (small animals).
• ± Deafness (unilateral).
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