Hearing, Vertigo, ETC...

Question 1

Sections of Normal Ear

Answer 1

• outer
• middle
• inner

Question 2

Transduction of Sound

Answer 2

• sound waves propagate in air, enter external auditory canal & bounce off tympanic membrane
• membrane moves malleus, incus, & stapes
• stapes mov. changes the pressure in the fluid filled inner ear and that triggers wave in the basilar membrane of the cochlea
• hearing by bone conduction: bone transmits vibration

Question 3

Transduction of Sound: at Cochlea

Answer 3

• hair cells with stereocilia are found in the organ of Corti, which rests on the basilar membrane
• hair cells are in contact with the tectorial membrane and are deformed by the traveling wave of sound
• high frequency tones maximally displace the basilar membrane near the base of the cochlea
• as freq. of sound dec., the point of maximal membrane displacement moves toward the cochlear apex
• distortion of the stereocilia on the hair cells causes depolarization of the cell & that results in inc. electrical activity along the auditory nerve

Question 4

Hearing Loss

Answer 4

• Very common
• all ages
• 1/1000 children: sig. hearing loss
• 10% of population has some hearing loss
• will inc. as population ages

Question 5

Causes of Conductive Hearing Loss

Answer 5

• transmission of sound through air is blocked
• may diff. causes: ear wax, foreign object in ear canal, otitis externa, tympanic membrane perforation, otitis media with effusion, otosclerosis

Question 6

Sensorineuroal Hearing Loss

Answer 6

• Disorders of the cochlear nerve, central pathways
• congenital
• prebyacusis - age related
• viral - mumps, measles, rubella, CMV, HIV
• ototoxicity: drugs
• trauma/surgery
• meniere’s disease
• vestibular Schwannomas (acoustic neuroma)

Question 7

Mixed Hearing Loss

Answer 7

• Otosclerosis involving the ossicles & the cochlea
• transverse & longitudinal temporal bone fx
• head trauma
• chronic otitis media
• cholesteatoma & middle ear tumors
• some inner ear malformations

Question 8

Meniere’s Disease

Answer 8

• dilated membranous labyrinth (hydrops)
• produces vertigo, fluctuating sensorineural hearing loss & tinntius
• dec. resorption of endolymaphatic fluid causes build-up or hydrops with high pressure, bowing & subsequent rupture in the membranse separating the endolymph from the perilymph
• 30min to several hrs until equilibrium is reestablished
• hearing loss persists & gradually worsens
• Treatment: low salt dies & diuretics can be helpful

Question 9

Clinical Assessment of Hearing Loss

Answer 9

• duration
• constant, progressive, fluctuating
• ear discharge
• otalgia
• tinnitus, vertigo
• family history - otosclerosis

Question 10

Hearing Loss Examination

Answer 10

• pinna (deformity)
• external auditory canal (obstruction)
• tympanic membrane
• middle ear space (aerated)
• pneumatic otoscopy
• Weber & Rinne
• Audiogram

Question 11

Rinne Test

Answer 11

• tell whether air conduction is greater than bone conduction
• normal: patient should hear sound in air after bone stops

Question 12

Weber Test

Answer 12

place on patients forehead

-if conductive hearing loss: sound will lateralize to that ear

Question 13

TM Perforation

Answer 13

• common & usually a consequence of infection
• trauma, including barotrauma, can perforate the membrane wall
• deg. of hearing loss depends on the size of hole

Question 14

Otosclerosis

Answer 14

• growth of abnormal bone around the otic capsule leads to fixation of the stapes resulting in a conductive hearing loss
• often accompanied by progressive sensorineural component
• starts in 20s to 30s and is bilateral
• family history +
• treatment is observation, hearing aid, or stapedectomy

Question 15

Vestibular Schwannomas

Answer 15

• Schwann cells, former designation of the tummor is preferable
• Meningiomas also occur in this spot
• present with sensorineural hearing loss & not with vertigo
• compression of the eight cranial nerve is so slow & gradual that the brain has adequate time for central compensation when the vestibular input dec. on one side
• by blocking visual fixation & provoking the semicircular canals, still detect the vestibular abnormality but that is a topic covered in a separate module on vertigo

Question 16

Dizziness

Answer 16

• 20% elderly patients experience is once a year that restricts activity & prompts physician visit
• Presyncope (faintness, lightheadedness)
• loss of balance, unsteadiness of gait
• Vertigo (spinning, swaying, illusion of movement)
• double vision, psychological dissociative feelings, vague sensations (hypoglycemia; drug intox. giddiness)

Question 17

Dizziness from Orthostatic Hypotension?

Answer 17

• lower body venous pooling (prolonged squatting)
• IV volume depletion
• medication effect
• autonomic neuropathy

-vasovagal reaction (neurocardiogenic syncope)

Question 18

Dizziness from Heart Diseases?

Answer 18

-ones that dec. cardiac output

• cardiac arrythmia
• congestive heart failure
• obstructed cardiac outflow (aortic valvular stenosis, cardiac tamponade, idiopathic hypertrophic subarotic stenosis (IHSS))
• pulmonary embolism

Question 19

Gait Imbalance in the Elderly

Answer 19

-neuronal loss due to aging or disease in networks that sub serve:
  cerebellar function (stroke, alcoholism)
  vestibular function (prior head trauma) 
  visual orientation (cataracts) 
  peripheral nerve function (position sense in legs)

Question 20

Elderly “Dizzy when I walk”

Answer 20

• neuronal loss due to aging or disease in networks that subserve: motor strength (stroke, cervical spondylosis), frontal lobe apraxia, basal ganglia (Parkinson’s, Lewy body dis, PSP, MSA), Arthritis & pain (hip & knees), inactivity & fear of falls
• drug toxicity & dehydration

Question 21

Psychiatric “Disassociation”

Answer 21

• feels distant from the real world
• home stressors
• past/current depression, panic attacks, anxiety, neurosis, psychosomatic personality
• family history of psychiatric disease
• hyperventilation for 3 min to reproduce symptoms (may activate seizure focus)
• neuropsych eval. Minnesota Multiphasic Personality Inventory (MMPI) detects somatization tendencies
• consult psychiatry

Question 22

“True” Vertigo

Answer 22

• Disease of vestibular system (central & peripheral)
• illusion of movement (whirling, spinning, swaying)
• often accompanied by nausea & vomiting
• Nystagmus (clinical sign): fast & slow components, defined by fast component (saccade), brain suppresses visual blur during saccade, vision possible only during slow phase of eye movement, room spinning to right to slow phase to left

Question 23

Yaw

Answer 23

-spin around the z-axis

Question 24

Specialized Vestibular “organs” act as motion transducers for?

Answer 24

• Translational motion (linear around x, y, z)

- Rotational motion (angular around x, y, z)

Question 25

How does the vestibular system monitor position?

Answer 25

-detecting angular (rotational), static & linear acceleration with specialized motion detectors

Question 26

Sacculus?

Answer 26

- coplaner with the vertical axis | - detect static head positions & linear accelerations in plane

Question 27

Utrical?

Answer 27

- coplaner with the horizontal axis | - detect static head positions & linear accelerations in plane

Question 28

What does the ampulla detect?

Answer 28

-rotational acceleration or deceleration within the plane of the canal

Question 29

Cupula

Answer 29

-located inside ampulla transduce this information for each semicircular canal

Question 30

Kinocilium

Answer 30

- tallest cilia in ear - depending on how it's bent, potassium channels in the tips of other cilia either open or close - cilia project into endolymph that is rich in potassium, K influx depolarizes the cell membrane which then activates Ca channels that open only when the membrane is depolarized - Ca influx activates Ca dep. K pumps that extrude the K into the K poor perilymph - allows for electrical resonance of the membrane to shift up or down in frequency & to modulate the conc. of Ca at the hair cell base - a rise in local Ca conc. triggers release of neurotransmitter

Question 31

Hair Cells in Utricle

Answer 31

- highly organized so that the kinocilium faces a midline valley called the stroila - mirror like arrangement - orientation curves by 90 deg. so that every movement in a 2D plane will be covered - head in neutral position, utricle is coplanar with ground

Question 32

Utricle Kinocilia Orientation

Answer 32

-toward the striola

Question 33

Saccule Kinocilia Orientation

Answer 33

-away from the striola

Question 34

Vestibular System & Eye Movements

Answer 34

- net inc. in firing from the left vestibular apparatus via Scarpa's ganglion causes the eyes to move to the right - acts as "pushing" muscle directing the eyes to the center, if one side is weak, the normal side will push the eyes toward the weaker side -if head suddenly turned left, the left horizontal semicircular canal will be stimulated & the right canal will be inhibited (reflex movement of eyes to right so that point of visual fixation is maintained: vestibulo-ocular reflex)

Question 35

Movement of Endolymph in the Canal

Answer 35

-cause either stimulatory or inhibitory response

Question 36

"True" Vertigo

Answer 36

- disease of one vestibular apparatus, 8th cranial nerve, vestibular nuclei, & associated pathways - uneven vestibular tone on eyes - ocular drift toward side of lesion (slow phase nystagmus) - mismatch with other sensory info. reaching cortex - corrective saccade from frontal eye fields (fast component of nystagmus) - Repetitive cycles (Nystgums - sign of vergigo) - Illusion of movement (whirling or spinning) - often accompanied by nausea & vomiting

Question 37

Gaze-Evoked Horizontal Nystagmus

Answer 37

- with extreme lateral gaze, normal people may show a few beats of nystagmus or even sustained nystagmus - induced with alcohol, sedatives, & anticonvulsant meds - direction change - no vertigo

Question 38

Ice Water Calorics

Answer 38

- ice water in external auditory canal causes a drop in the tonic vestibular firing rate - other ear continues to fire at baseline rate (2 sides are unequal now) - normal side pushes the eyes toward the side of ice water irrigation

Question 39

Motion Sickness

Answer 39

- mismatch b/w what eyes report to brain & the vestibular feedback - induces vertigo, nausea, & vomiting - visual fixation suppresses vertigo due to vestibular-visual imbalance or mismatch

Question 40

Frenzel Lenses

Answer 40

- 20 diopter lenses eliminate visual fixation | - magnify & illuminate the eyes

Question 41

History for Dizziness

Answer 41

-describe -time course -effect of position, triggers? -History & Review of Systems: otologic, cardiac, psychiatric, neurological -Drug toxicity: anti-HTNs, dopamine agonist - orthostasis sedatives & anticonvulsants - gait dysequilibrium amninglycosides - otoxocity

Question 42

Physical Exam for Dizziness

Answer 42

- Orthostasis - Cardiac Murmurs & Arrhythmias - Visual loss - peripheral sensory loss - gait disturbance - brainstem/cranial nerve deficits associated with central vertigo

Question 43

Neuro-otoogic Exam

Answer 43

- inspect tympanic membranes - check hearing, Weber & Rinne tests - Extra-ocular eye movements: nystagmus - Thwart visual fixation (Frenzel lenses, cover the visually fixating eye during funduscopy) - Maneuvers that provoke & detect vestibular imbalance: head thrust maneuver, head shaking nystagmus, Dix-Hallpike maneuver

Question 44

How to see subtle nystagmus without Frenzel lenses?

Answer 44

-close other eye during funduscopy, to eliminate visual fixation and watch the optic disc jiggle

Question 45

Head Thrust Maneuver

Answer 45

- tests for dec. in the vestibulo-ocular reflex or VOR - sudden turn of the head stimulates one horizontal semi-circular canal while inhibiting the other - this causes a reflex compensatory movement of the eyes in the opposite direction via the pathways shown eariler

Question 46

How to stimulate the horizontal semi-circular canals?

Answer 46

- tilt head forward 30deg. to make the canals coplaner with the floor - start continuous side to side shaking for 20 sec. then stop

Question 47

Semicircular Canals

Answer 47

-Posterior, Anterior, Horizontal (right & left)

Question 48

Dix-Hallpike Maneuver

Answer 48

-to maximally stimulate the left posterior canal & inhibit the right anterior canal, the head is turned to the left by about 45 deg. and the patient lies down backwards from a sitting to a lying position

Question 49

Peripheral Vertigo with Nystagmus: Dix-Hallpike

Answer 49

- 5-20 sec. latency of onset - subsides over 1-2min (improves w/visual fixation) - Nystagmus inc. with gaze away from lesion - Usually mixed horizontal (torsional (horizontal predominating)) - Habituates with repetition

Question 50

Central Vertigo with Nystagmus: Dix-Hallpike

Answer 50

- no latency of onset - Sustained with position (does not improve with visual fixation) - no inc. but may change direction with change of gaze - usually single plane nystagmus (horizontal, vertical or torsional) - does not habituate - other brainstem deficits

Question 51

Benign Paroxysmal Positional Vertigo (BPPV)

Answer 51

- Dix-Hallpike makes diagnosis - otoconia embedded in utricle break free of the gelatinous membrane with age or trauma, the post. semicircular canals are the most dependent during sleep these displaced particles (Ca carbonate) collect in these canals (1 or both), forms sludge that can plug up canal lumen so when head movement involves affected post. canal there is a slump-like action that produces greater pressure than normal - causes greater distortion of the cupula in the ampulla & the canal signals the brain that the head has rotated posteriorly faster & more than it has -vertigo starts 5-10 sec. after head movement and lasts for 30-45 seconds

Question 52

How is Benign Paroxysmal Positional Vertigo Cured?

Answer 52

-canalith reposition (Epley) maneuver

Question 53

Cupulolithiasis

Answer 53

- less common cause of BPPV | - particles can reach the cupula & cause distortion there

Question 54

Vestibular Neuritis

Answer 54

- Postulated viral infection (HSV1 viral reactivation) - Severe Vertigo, nausea, vomiting - Gait: veers toward affected ear early-on - Positional changes not tolerated - Ice-water in normal ear provides immediate (temporary) relief - Labyrinthitis is the term used if hearing is also affected

Question 55

Vestibular Neuritis Symptomatic Relief

Answer 55

- benzodiazepines, meclizine, scopalamine patch, antiemetics - IV Methylprednisolone speeds recovery - central compensation over 1-2 weeks