Lecture 14 Flashcards
Describe vestibular evoked myogenic potentials (VEMPs)
-evoked by short duration auditory tones or clicks (via headphones)
-sounds stimulates primarily the utricle and saccule (otilith organs close to cochlea-sensitive to auditory inputs)
-influence both vetibulo-spinal and vestibulo-ocular pathways
-auditory clicks or tone burst evoke a muscular reponse in tonically active muscles- can test differnt pathways and reflexes e.g. to sternocleidomastoid, muscles of eye, soleus.
Differentiate vetibular lesions
-peripheral vestibular lesions- damage to labryths or vestibulo-cochlear nerve (VII) e.g. peripheral part of vestibular system
-central vestibular lesions- damage to vestibular nuclei or pathways projecting to brainstem, thalamus or cerebellum
Identify uni-lateral vestibular lesion symptoms
-vertigo
-neusea
-postural instability
Describe vertigo
-due to spontaneous nystagmus
Descrive normal head turning vs vestibular damage in relation to vertigo symptoms
- in normal head turning to the right, hair cells pulled left, increased firing rate on right side, eyes move to left
-with damage to left semicircular canal, decreased firing rate on left side which causes a differential in signal when head is still, interpreted as head rotation to right, eyes move left (VOR) in opposite direction which triggers nystagmus
-over time get plastic changes, system reaslises abnormalities and adapts to new normal-> central compensation
How can nystagmus occur
In various planes of movement e.g. horizontal, or torsional
Reasons for neusea
- sensory mismatch or conflict e.g. vestibular system giving signal head is moving, but different to proprioceptive sense
-vestibular-autonomic connections e.g. excessive excitation of autonomic system
Causes of postural instability
-unbalanced balance reflex, abnormal signal of left/right
-loss of awareness/orientation in space
Describe testing for postural stability
rhomberg test, fakuda test/unterburger test, dynamic posturography
Describe the rhomberg test for testing balance
-feet together, eyes closed, should see a sway or fall in direction of lesion e.g. right lesion, right fall
Describe fukuda test
arms in front eyes closed, march on spot ~30 secs, start to turn in direction of side of lesion
Describe problems associated with balance tests
s-many other systems involved in balance control just balance respone isnt enough on own to indicate vestibular deficit
Describe abnormal VOR and how to identify it
Normally eyes equal and opposite to movement of the head. With abnormal see a differnt pattern. With acute vestibular deficit it rotate head in one directed, decreased or abnormal VOR, unable to respond to stimulus of head in direction that would activate vestibular receptors. Right side normal VOR response, opposite side abnormal VOR reponse identified by two features, E.g. eye has too small compared to head velocity (lags behind) and therfore to get eye back on target have second sacade correcting eye back to target. Get abonormal VOR when move head to left, left side is usually excited, and drives VOR, abnormal response indicates left sided deficit.
Can also have bilateral deficits, small change in eye velocity relative to chair velocity (rotating chair test)
Describe abnormal VEMPs
If have damage to vestibularocular nerve or otilith organs, abnormal VEMP responses. In normnal case is stimulate right ear expect normal VEMP on right ipsilateral neck muscle and normal vemp on contralateral eye muscle. If damage right side e.g. right side vestibular lesion, absence of VEMP in ipsilateral neck (right absence of cervical VEMP) and contraleteral eye muscle (left absence of ocular VEMP).
Identify causes of uni-lateral vestibular lesions
-tumors
-vestibular neuritis
-surgery
-menieres disease
-perilymph fistula
-benign parxysmal peripheral nystagmus (vertigo): most common symptoms
Describe tumor how (uni-lateral vestibular lesions)
-acoustic neuroma, tumor grows around vestibulocochlear nerve, can grow and impinge on nerve
-e.g. Cerebellar ponstine angle tumor, surgical removal can damage nerve
Describe vestibular neuritis (uni-lateral vestibular lesions)
-viral infection iof vestibular nerve
-mainly affects 30-60years of ages which triggers symptoms e.g. vertigo, neasuea, balance.
-lasts days to weeks
-if persistant can use exercises to compensate for imbalance
Describe surgery (uni-lateral vestibular lesions)
-labrinthectomy (chemical or surgical damge to labyrynth) e.g. by plugging canals to block fluid or antibiotic which damages hair cells to improve imbalance, can cause one sided damage
-vestibular nerve section: e.g. removing tumors may have to resect nerve, hearing loss on one side
Describe meniers disease
-vestibulara dn hearing deficits affect adults 40-60yrs
-key feature, eposidic (minutes-hours): first feel fullness in hear, hearing loss, tinnitus, necxt get vertigo, nausea, impbalance and drop attecks, which eventually subside and return back to normal
mechanism of meniers disease
-increased endolymph volume and pressure
-small ruptures of membranous labarynth causing endolymphatic hydrops, problem with circulation of fluid to endolymphatic sac
-mixing of endolymph and perilymph fluid, chemical ionic changes
Causes of meniers disease
unknown- viral/ autoimmune/genetic
treatment for menieres disease
lifetyle changes, e.g. diet (increased salt, caffeine, alcohol trigger episodes), reduce stress; surgery which damages side of system allows it to compensate
Describe cause of perilymph fiscula
traumatic injury or sever pressure damage e.g SCUBA
Decsribe perilymph fistula
- round/oval window ruptures allowing pressure changes to affect inner ear, perilymph fluid leads out
- treated with rest aor surgery
- abnormal nystagmus triggered by additiobnal pressure can use fistula test (air filled bulge increase pressure in inner ears- look for vertigo
Causes of benign paroxysmal peripheral nystagmus (vertigo)
due to trauma or age
Describe benign paroxysmal peripheral nystagmus (vertigo)
-charcterised by brief attacks of vertigo triggered by change in head orientation
-otoconia dislodged and free in canal (usually posterior canal), as tip head, otoconia slide downh canal which generates current which triggers vertigo, then eventually settles
- identified with dix-hallpike maneauver (clinical test)
- treated with physical therapy (epley maneauver) if it doesnt resolve
Common symptoms of bilateral vetsibular loss (BVL)
-postural instability (without vision)
-blurry vision (when moving and fixating)
causes of bilateral vestibular loss
-ototoxis medication- gentamicin (up to 50% of BVL) which treats bacterial infections
-meningitis
-menieres disease (bilateral)
Describe central vestibular lesions
-optokinetic reflex involves medial vestibular nucleus, can be identified by opto-kinetic nystagmus test
-adjusts eye movemenst to reduce retinal slip
-can use combination of tets to indicate whether lesion in peripheral or central e.g. VOR and optokinetic reflex
Describe optokinetic and VOR reflex pathways and how to determine damge
- vestibular nuclei central to both pathways.
- If damge vetibular system, vestibular nuclei is intact, abnormal VOR response, normal optokinetic reflex
-If damage central abnormal VOR and abnormal optokinetic reflex
