Vestibular disease in small animals: causes and diagnosis

This article discusses Vestibular Disease in dogs and cats, focusing on central versus peripheral signs. It details neurological examinations for differentiation, including mental status, nystagmus, and cranial nerve involvement. Causes range from inflammatory to neoplastic conditions. Diagnostic tests such as MRI, otoscopic exams, and brainstem auditory evoked responses (BAER) are helpful to make a definitive diagnosis.

Identifying central versus peripheral vestibular signs

Recognition of vestibular signs and differentiation between central and peripheral vestibular disease is essential to be able to formulate an adequate differential diagnosis.

Abnormal findings on a neurological examination can assist in differentiating between a central and peripheral vestibular lesion, as listed in the table below:

	CENTRAL VESTIBULAR SIGNS	PERIPHERAL VESTIBULAR SIGNS
Mental status	Abnormal (disoriented and or obtunded)	Normal or disoriented
Posture	Head tilt towards the affected side* Broad based stance	Head tilt towards the affected side
Gait	Ataxia, tendency to fall/lean/veer/stumble/fall/roll to affected side*	Ataxia, tendency to fall/lean/veer/stumble/fall/roll to affected side
Postural reactions	Deficits in ipsilateral limbs	Normal
Nystagmus	Any direction, but vertical or changing direction more common	Horizontal or rotary with fast phase directed opposite to the other vestibular signs
Strabismus	Ventral positional – ipsilateral to lesion*	Ventral positional – ipsilateral to lesion
Other cranial nerves affected	Multiple cranial nerves can be affected (V to XII most likely): most common signs are decreased facial sensation and masticatory muscle atrophy (V) and facial paresis/paralysis (VII). Other possible signs: dysphagia (IX-X), fixed strabismus (VI), or lingual atrophy (XII).	Signs from dysfunction of the sympathetic innervation of the eye  (Horner’s syndrome) and/or CN VII (facial paresis/paralysis), ipsilateral to the lesion

*With paradoxical vestibular disease (uncommon CENTRAL presentation caused by lesions affecting the caudal cerebellar peduncles or flocculonodular lobes of the cerebellum), the vestibular signs - head tilt, strabismus and vestibular ataxia - are opposite to the side of the lesion, but postural reaction deficits are ipsilateral to the lesion.

Most common causes of central vestibular disease in small animals

Any disease process affecting the brainstem area (rostral medulla oblongata) where the central vestibular structures (vestibular nuclei) are located, or the flocculonodular lobes and/or fastigial nuclei of the cerebellum can cause central vestibular signs. The likelihood of one or another disease process will be determined by the patient’s signalment (breed, sex, age) and the history (acute, rapidly progressive, chronic signs or episodic). The main causes of central vestibular disease according to presentation, are:

• Inflammatory CNS disease (MUO)
• Vascular disease (cerebrovascular accidents – infarcts mainly)
• Toxic (metronidazole toxicity)
• Traumatic (head trauma)
• Nutritional (Thiamine deficiency)

• Degenerative diseases (cerebellar cortical degeneration)
• Neoplasia (primary or secondary-metastatic)
• Anomalous conditions (intra-arachnoid cysts, dermoid-epidermoid cysts)

Most common causes of peripheral vestibular disease

The peripheral vestibular system (vestibular division of CN VIII and vestibular receptors) is located in the inner ear, so any disease process affecting the inner ear structures can cause peripheral vestibular signs.

The two most common diseases causing peripheral vestibular signs are:

• otitis media/interna
• idiopathic vestibular disease.
  
  

Other less frequent causes include:

• Congenital vestibular syndromes in puppies
• Nasopharyngeal polyps in cats
• Neoplasia affecting the middle/inner ear structures 
• Toxins (aminoglycosides, furosemide, chlorhexidine)
• Trauma (iatrogenic during ear flushing/skull fractures)

Diagnostic tests for dogs and cats with vestibular disease 

It is essential, before performing specific diagnostic tests, to clinically differentiate peripheral from central vestibular disease.

In all cases, a minimum database before performing specific tests under anaesthesia should include: 

• CBC

• Serum biochemistry

• Urinalysis

• Thoracic radiographs, abdominal US or CT of the thorax and abdomen  in middle to older-aged animals to explore for systemic diseases that could be related to the neurologic signs (infection, neoplasia, etc.)

Tests for central vestibular disease:

• MRI to evaluate the brain structures in the caudal cranial fossa (cerebellum and medulla oblongata), followed by 

• CSF tap and analysis, if feasible, is especially helpful in the diagnosis of infectious/inflammatory CNS disease 

Tests for peripheral vestibular disease:

• Otoscopic ear exam (external ear canal)

• CT or MRI of the middle/inner ear structures

• Myringotomy if fluid or solid content is identified in the affected tympanic bulla, with aspiration of content for cytology and culture/sensitivity

• Brainstem auditory evoked responses (BAER) if available to assess function of the peripheral and central auditory pathways (closely associated with the vestibular ones

The neurology of balance: Function and dysfunction of the vestibular system in dogs and cats. Kent M, Platt SR, Schatzberg J. The Vet J 185 (2010) 247-258

Vestibular disease in dogs and cats. Rossmeisl Jr JH. Vet Clin Small Anim 40 (2010) 81-100