The Vestibular Patient Flashcards
Physiologic functions of the vestibular system
Maintenance of posture and balance relative to the head and rest of the body. Does this by detecting rotational movement, linear acceleration/deceleration, rapid corrective eye mvmts. (occulocephalic reflex)
Peripheral vs. Central Vestibular System
- Peripheral (outside the brainstem): middle (tympanic membrane) & inner ear (vestibular apparatus)
- Central (within the CNS): CNVIII vestibular axons that travel in/to the brainstem, SC, cerebellum, vomiting center, cerebrum
CNVIII is a combo of vestibular & auditory axons
Vestibular axons from the vestibular nuclei in the brainstem project caudally to the SC (vestibulospinal tracts– promote limb extensor tone and inhibit flexor tone on ipsilateral side), rostrally within the brainstem (medial longitudinal fasciculus– eye position), caudally within the brainstem (medial vestibulosponal tract– maintain positioning of body/limbs relative to head), to the reticular formation of the medulla (V+ center), and to the cerebrum (thalamic relay nuclei– conscious awareness of body’s position in space).
How does the peripheral vestibular system function?
1. Semicircular canals
2. Utricle & Saccule
- Semicircular canals: fluid-filled tubes of inner ear that detect head position relative to ROTATIONAL angular mvmts.
- Utricle & Saccule: sacs within the inner ear that localize STATIC position of head (spatial orientation) and detect linear acceleration/deceleration (utricle = horizontal, saccule = vertical)
What are the respective receptors of the semicircular canals and utricle/saccule? What are their roles?
- Semicircular canal: Ampulla (crista ampullaris) – covered in hair cells that become displaced as endolymph within the canals move in relation to outside forces
- Utricle/Saccule: Macula – covered in hair cells that become displaced as statoconia on otolithic membrane move relative to gravitational forces
BOTH stimulate vestibular portion of CN VIII
Pathophysiology of a lesion in the body’s (central) vestibular apparatus
Normal: Excitement of the vestibular nuclei in the brainstem causes ipsilateral facilliation of extensor tone and contralateral facilitation of flexor tone of muscles in limbs/trunk (balance)
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LESION: a lesion prevents activation of the ipsilateral side (lack of extensor tone) while the contralateral side functions like normal -> body pushed in direction of lesion due to normal extensors on contralateral side
Clinical signs of vestibular dysfunction (4)
- Abnormal posture
- Vestibular ataxia (incoordination)
- Strabismus
- Nystagmus (ventral/ventrolateral)
How to clinically localize peripheral vs. central vestibular disease
Accurate hx + physical & neuro exams; use of CS to try and isolate signs that can only be explained by a central (brain) vestibular lesion
Presence of CN deficits besides VII and VIII, vertical nystagmus, positional nystagmus, behavioral changes, mentation changes, seizures, and proprioceptive defictis are what type of vestibular disease?
Central
- recall that vestibular projections go to cerebrum/forebrain
Facial nerve paralysis can be seen with what type of vestibular disease?
Peripheral
- CN7 and CN8 travel very intimately together when entering the petrous part of the temporal bone via the interal acoustic meatus
- Disease processes like otitis or trauma may affect CN7 function (partial or complete facial nerve paralysis or spasm)
Horner’s Syndrome can be seen with what type of vestibular disease?
Peripheral
- sympathetic innervation to the eye passes in close contact with middle & inner ear structures
- peripheral dz can manifest as ipsilateral Horner’s syndrome
A dog presents with vestibular ataxia. What could be a signs on neuro exam that they have central vestibular disease over peripheral?
- If the strength of their gait is negatively affected (tetra- or hemiparesis)
- If there are deficits in postural reactions (will be ipsilateral)
- Nystagmus is vertical and positional
- Multiple CN deficits (besides 7&8)
Peripheral: horizontal/rotary nystagmus
Central: horizontal/rotary/VERTICAL nystagmus
What direction is the fast phase in nystagmus with vestibular disease?
AWAY from lesion for both peripheral & central
central can be towards, but normally away
When the vestibular apparatus is damaged on one side, there is an imbalance of neural activity in the vestibular nuclei because the vestibular apparatus on the normal side continues to supply the vestibular nuclei with a constant signal. This imbalance is “interpreted” by the brain stem as rotation or movement of the body. A nystagmus will be generated, even though the body and head are stationary, with the slow phase directed toward the side of the lesion. By convention, the nystagmus is described by reference to the fast phase.
Dx approach for peripheral vestibular disease
- Otoscopic exam
- Tympanic bulla rads (DV, open-mouth)
- CT
- BAER test
- Myringotomy (cytology, culture)
Dx approach for central vestibular disease
- MRI
- CSF tap/analysis
- Referral to neuro
Top Ddx for peripheral vestibular disease (5)
- Otitis media/interna
- Inflammatory polyps
- Aural neoplasia
- Idiopathic vestibular disease (vestibular neuronitis)
- Toxicity (damage to ampulla or macula)
Top Ddx for central peripheral disease (6)
- Inflammatory/Infectious (CDV, FIP, tick-borne, toxo, fungal, MUE)
- Hypothyroidism
- Intracranial neoplasia
- Thiamine (B1) deficiency
- Toxicity
- Cerebrovascular disease
How to treat otitis media/interna
Oral ABX +/- myringotomy
- clavamox, baytril
- caution w/ topical otic meds (can irreversibly damage hair cells)
Staph, Strep, Pseudomonas, Proteus, Malassezia pachydermatitis
PSOM in Cavalier King Charles Spaniels: what is it plus tx
Primary Secretory Otitis Media: non-infectious cause of otitis media/interna
- accumulation of viscous mucus plug within one/both middle ear cavities (discomfort + otitis media signs- head tilt, CN7 dysfunction)
- tx = myringotomy
Myringotomy: indications + basic details or procedure
- Indicated when the TM is intact yet there is clinical and bulla imaging evidence of otitis media
- Caudo-ventral approah: needle inserted into TM and fluid is aspirated for cytology and C/S
What is a common cause of otitis media/interna in cats? Tx?
Inflammatory polyps originiating form middle ear and/or nasopharynx
- Tx = removal with traction or bulla osteotomy
https://criticalcaredvm.com/nasopharyngeal-polyps-cats/
How can PNS neoplasms result in peripheral vestibular disease?
compression or invasion of CN8
- ceruminous gland adenocarcinoma = 1º ear tumor
- invasion: fibrosarcoma, chondrosarcoma, osteosarcoma, SCC
Idiopathic Vestibular Disease
1. Signalment
2. Presentation
3. Key characteristics
4. Prognosis
- Adult cats; geriatric dogs
- Acute-peracute onset signs of peripheral vestibular disease
- Unilateral clinical signs; mild head tilt to severe imbalance/rolling; horizontal/rotary nystagmus; assymetrical ataxia
- Most animals improve rapidly; complete recovery 2-3 weeks. Tx goal = supportive tx (sedatives, antinausea)
found to be worse in july/august in cats– aberrant cutebra larval migrans??
Why is ototoxicity a guarded prognosis?
Damage to hair-cell receptors is irreversible
What is the proposed pathophysiology of hypothyroid-related central vestibular disease?
Infarction 2º to atherosclerosis (plaque buildup in arteries) or CNS demyelination
Most common intracranial neoplasms causing central vestibular disease in dogs vs cats
Dogs: meningiomas, choroid plexus tumors
Cats: Meningiomas, lymphomas
How can thiamine deficiency (VitB1) cause central vestibular signs (cats)?
Incomplete TCA cycle (role of B1) results in necrosis, spongiosis, and hemorrhage in brain stems
TCA cycle: mitochondrial hub for production of CHO, AA, FA
What drug is known to induce central vestibular signs at toxic doses?
Metronidazole
- when doses exceed 60 mg/kg/day
