Vestibular disease Flashcards
What is the role of the vestibular system
The main function of the vestibular system is to adapt the position of the eyes and the body with respect to the position and movement of the head
What is the anatomy of the peripheral vestibular system
Information from receptors located in the inner ear (within the petrous temporal bone) travel along the vestibular nerve (along with the cochlear nerve) into the cranial vault via the internal acoustic meatus
The vestibulocochlear nerve then travels along the lateral surface of the medulla to the cerebellomedullary angle
What is the anatomy of the central vestibular system
The vestibulocochlear nerve enters the medulla between the caudal cerebellar peduncle and the trigeminal nerve
The majority of the vestibular fibers terminate in one of four bilateral vestibular nuclei within the medulla and pons
What clinical signs are common to all lesions of the vestibular system
Common to all lesions of the vestibular system is a loss of balance and vestibular ataxia characterized by:
- spontaneous nystagmus
- head tilt
- circling
What is the pathomechanism for unilateral peripheral vestibular disease
Unilateral lesions within the inner ear, causing disruption of the vestibular receptors, vestibular ganglions and vestibular portion of cranial nerve VII, typically cause asymmetrical ataxia without loss of strength
There is no loss of proprioception, and if supported, the cat can bear weight on the limb (indicating intact LMN) and move it rapidly (indicating intact UMN)
What are the position of the head and trunck in a cat with vestibular disease
The cat’s head is tilted towards the affected side
The cat’s neck and trunck will tend to lean or fall in the same direction, often in tight circle if it is ambulatory
What is the pathomechanism supporting head tilt and circling in vestibular ataxia
Vestibular ataxia is due to the loss of extensor muscle stimulation and flexor muscle inhibition to the ipsilateral limbs with the contralateral limbs having this input preserved
Typically, with peripheral disease, the head tilt and ataxia are most severe within the first 24-48 hours, after which time the cat starts to compensate
- blindfolding may make the signs worse again
How would you characterize the nystagmus in a cat suffering peripheral unilateral vestibular disease
In unilateral peripheral vestibular disease, the fast phase of the nystagmus is directed away from the side of the lesion and is typically horizontal or rotatory
The rate and severity of nystagmus tend to be worse with peripheral vestibular diseases
How would you characterize the strabismus observed in vestibular diseases
The presence of ventral or ventrolateral strabismus when the head and neck are held in extension may also indicate vestibular disease
- the strabismus is on the same side as the vestibular lesion
- positional strabismus (induced when the head is held dorsally) is more frequent than spontaneous strabismus (always present)
What are the two types of nystagmus that can be observed with vestibular disorders
Spontaneous nystagmus
- present with a normal head position
Positional nystagmus
- present when the head is in certain position
How are the postural reactions in a cat with vestibular disorder
Lesions of the peripheral vestibular system do not interfere with limb movement
- hopping, hemi-walking and paw placement should all be normal
What can you conclude if a cat has a peripheral vestibular disorder associated with concurrent ipsilateral facial nerve deficit and/or Horner’s syndrome
The presence of concurrent ipsilateral facial nerve deficit and/or Horner’s syndrome generally indicates the presence of middle ear disease
- although this was also reported in one cat with idiopathic peripheral vestibular disease recently
What is the cause of bilateral peripheral vestibular disease
The cause of bilateral peripheral vestibular disease is bilateral otitis media/interna
Explain why it could be difficult to diagnose a cat with bilateral peripheral vestibular disorder
This can be hard to diagnose as:
- no postural asymmetry or spontaneous nystagmus is observed
- these animals typically assure a crouched position and have a slow and tentative gait, with their head swaying widely from side to side and they may rock their body slightly from side to side
Since there is a loss of vestibular input to both eyes, there will be an absence of physiological nystagmus
What observation regarding nystagmus would suggest a central vestibular disease
Nystagmus that changes direction with different head positions is indicative of central vestibular disease
The presence of vertical nystagmus makes central vestibular lesion more likely but it is no more thought to be pathognomonic for central lesions
What is the main clue for the presence of a central vestibular lesion
The main clue to the presence of a central lesion is the finding of ipsilateral (or bilateral) postural reaction deficits +/- spastic paresis/paralysis (UMN signs)
- may have altered mentation
- may have multiple concurrent unilateral or bilateral cranial nerve deficits (CN V, VII, IX, X and XII)
What is a paradoxical vestibular disease
Paradoxical vestibular disease is an uncommon central vestibular condition that causes head tilt and loss of balance away from the side of the lesion
This is typically seen with lesions located in the caudal cerebellar peduncle (or more rarely, the floculonodular area of the cerbellum)
- such lesions may be infarcts, tumors or inflammatory conditions
What is the consequence of a lesion in the caudal cerebellar peduncle
A lesion in this area results in loss of inhibition of the vestibular nuclei on this side
On a neurological exam, there will be signs of central vestibular disease, however with a lesion involving the caudal cerebellar peduncle, the loss of conscious proprioception and UMN signs will be in the limbs opposite to the direction of the head tilt
- the spinal signs will be on the same side as the lesion
What would be your diagnostic plan for a peripheral vestibular disorder
Examine ears, caudal nasal cavity, and oropharynx under general anesthesia
- preferably with video-otoscope and retroflexed endoscope)
Serum cryptococcal antigen test
- cryptococcosis has been reported to cause peripheral vestibular disease
Bulla radiography (open-mouth view) or CT scan (more sensitive)
+/- myringotomy for the collection of samples for cytology and microbiology (culture and sensitivity)
+/- collection of material for histopathology
- direct biopsy using cupped aligator forceps or surgical biopsy via bulla osteotomy
What would be your diagnostic plan for a central vestibular disorder
Chexk dietary history for evidence of thiamine deficiency
- +/- trial course of Vitamin B1
Advanced imaging
- MRI is better for the brain stem +/- CSF analysis
Serology for cryptococcus and toxoplasma
What are the main causes of peripheraal vestibular dysfunction
Otitis media-interna
Nasopharyngeal polypd
Benign idiopathic feline vestibular syndrome
Congenital vestibular dysfunction in Siamese and Burmese kittens
Neoplasia
Toxicity
Trauma
What are the main features of benign idiopathic feline vestibular syndrome
Etiology is unknown
- it is hypothesized that the condition may be due to alterations in endolymphatic flow or the electrolyte concentrations of perilymph
Risk factors:
- Acute viral URT infection can precede this condition in some cats
- increased frequency in July and August in the USA
- no breed or sex prediclection
- it can occur at any age
Clinical signs
- the condition is generally acute or per-acute in onset (less than 24h)
- signs similar to other peripheral vestibular disorders
- normally there should not be evidence of Horner’s syndrome or facial nerve paralysis
Diagnosis is based on the exclusion of other causes of peripheral vestibular disease
Treatment is purely supportive
- signs tend to abate over 1-4 weeks
- rarely some cats have a residual head tilt
Explain how a cat can contract otitis interna
Bacterial otitis interna (labyrinthitis) is usually a result of otitis media/externa
- it is a common cause of peripheral vestibular dysfunction
Otitis media may also result from an extension of infection from the nasopharynx, via the eustachian tube
- cases of otitis media secondary to cryptococcosis have been reported
What is the treatment for otitis media/interna
Treatment with a 6 week course of an appropriate antibiotic is usually required
Some cases may need surgical drainage bulla osteotomy if unresponsive to medical therapy
What are the key features of congenital peripheral vestibular dysfunction
Congenital vestibular dysfunction has been reported in Siamese and Burmese kittens
- the cause is unknown (hereditary trait or acquired developmental abnormality)
Signs of peripheral vestibular dysfunction are noted when kittens are about 3-4 weeks of age
- kittens lean to compensate
- signs of improvement are generally noted by 3-4 months of age
- affected kittens may have concurrent deafness
What kind of neoplasia can induce peripheral vestibular signs
Tumors of the middle and inner ear may produce signs of peripheral vestibular dysfunction
- typically tumors affecting the petrous temporal bone and tympanic bulla also cause signs of facial nerve dysfunction
What is the origin of nasopharyngeal polyps that can cause peripheral vestibular dysfunction
Inflammatory polyps originating from the epithelium of the middle ear or eustachian tube may cause signs of peripheral vestibular dysfunction
What are the clinical signs associated to peripheral vestibular dysfunction in a cat with nasopharyngeal polyp
Affected cats may also have signs of
-facial nerve paralysis
- Horner’s syndrome
- otitis externa/media
- nasopharyngeal obstruction
It will depend on the location and size of the polyp
Which toxic can cause peripheral vestibular dysfunction
Ototoxicity leading to peripheral vestibular dysfunction (+/- deafness) can be caused by:
- systemically administered drugs (via the hematogenous route)
- topical agents applied into the external ear canal
A ruptured eardrum makes ototoxicity more likely
Potentially ototoxic drugs:
- aminoglycosides
- furosemide (reported in humans only)
- topical ear canal cleaners (even saline flushes)
- intra-aural fipronil
How can you evaluate dysfunction of the cochlear nerve
Dysfunction of the cochlear nerve can be evaluated by electrodiagnostic testing (BAER)
What kind of trauma can result in peripheral vestibular dysfunction
Damage to the petrosal part of the temporal bone or the tympanic bulla can result in signs of vestibular dysfunction
What will be your differentials for central vestibular dysfunction
Neoplasia
Infection
Toxicity
Trauma
Explain how neoplasia can cause signs of central vestibular disease
Neoplasia can cause signs of central vestibular disease by/
- direct involvement of the brainstem
- causing an increased intracranial pressure resulting in cerebellar herniation through the foramen magnum
- causing obstructive hydrocephalus of the fourth ventricule
What are the main infectious causes of central vestibular dysfunction
Infections of the CNS can potentially cause signs of central vestibular dysfunction
- either alone or as part of a multifocal disease process
Bacterial meningoencephalitis may arise secondary to otitis media/interna
FIP, toxoplasma and cryptococcosis can also cause central vestibular dysfunction
What are the two main toxic causes of central vestibular dysfunction
Administration of high doses of metronidazole (>50 mg/kg, q24h for more than 5 days) has been reported to cause diffuse neurological dysfunction, including seizures and signs of central vestibular disease
- treatment includes supportive care and cessation of the drug
- prognosis is generally favorable
Signs of central vestibular dysfunction have been reported in cats with lead toxicity
- although anorexia, vomiting and seizures are more commonly observed
- exposition most commonly arises secondary to ingestion of paint flecks caught on the coat during the renovation of older properties
Explain how head trauma can lead to central vestibular dysfunction
Head trauma may result in central vestibular dysfunction either due to:
- direct damage to the brainstem
- secondary to elevated intracranial pressure resulting in herniation of the cerebellum through the foramen magnum
