77. Posture & Dizziness

Question 1

What are the inputs to brain circuitry for balance?

What is nystagmus?

Answer 1

Inputs: Vestibular System, Vision, Somatosensory (Proprio)

Nystagmus: rhythmic pattern of slow/fast phases of eye movement
described by direction of fast movement (from patient’s frame of reference)

Question 2

What is the physiology of inner hair cells?

Answer 2

Motion sensors = convert motion (acceleration) into electrical signal
-tonically firing at baseline
-POLARIZED: bend in one direction increases AP rate, opposite direction decreases AP rate
-PAIRED with cells in other ear with opposite Polarity
Creates “PUSH-PULL” relationship for rotational acceleration - ipsi ear increases AP rate, contra ear decreases AP rate

Vestibular nuclei in brainstem: process difference in firing rate - send signal to oculomotor nuclei to drive eye movements (via CN 6 nucleus to CN 3 nucleus)

Question 3

Vestibular Neuritis

• what is it
• CP
• Pathophys
• tx

Answer 3

Inflammation of vestibular nerve (unknown cause)
CP: abrupt onset, severe spinning, constant, steadily improving, directional nystagmus
PP: damage to vestibular nerve = decrease firing rate = vestibular nuclei think head is rotating contralaterally = send eye signals to move ipsilaterally (slow drift toward affected side and snap back to target)

Tx: acute tx sx - vestibular suppressants (meclizine, clonazepam), anti-emetics (odansetron for nausea)
later: vestibular rehabilitation therapy - STANDARD OF CARE (accelerates recovery, helps pt get back on their feet faster)

Question 4

Benign Paroxysmal Positional Vertigo (BPPV)

• CP
• Pathophys
• What is the Dix-Hallpike Maneuver
• Nystagmus features
• Tx

Answer 4

CP: older age onset, abrupt onset of brief moderately intense spinning, re-triggered with head positioning
PP: otolith from utricle/saccule breaks loose, enters semicircular canal, excessively stimulates hair cells = dizziness/nystagmus
Dix-Hallpike: turn head and lay back triggers nystagmus (rock the otolith)
Nystagmus: has horizontal, vertical, torsional components due to involving obliquely oriented posterior canal (most common canal)
Tx: vestibular maneuvers- use gravity to put otolith back (Epley maneuver for posterior canal - most common)

Question 5

Physiology of Multisensory Integration of Balance inputs

Answer 5

Brain takes vestibular fx, vision, somatic sensation (proprio) to understand body’s orientation
Brain collects and processes all these inputs

Question 6

Gentamicin Ototoxicity

• CP
• Pathophys
• Tx

Answer 6

CP: recent gentamicin/ABx use, chronic unsteadiness standing (slowly improvin) - worsens in dark rooms on soft surfaces
PP: Gentamicin is vestibulotoxic - accumulations persist weeks after use - cause bilateral vestibular weakness/loss - hair cells do NOT regenerate - never restore fx
Patients recover by brain compensation - greater reliance on vision/proprio (why sx worsen w/o vision/proprio)
tx: Time (for compensation), Vestibular rehab tx (accelerates recovery, but cannot change outcome)

Question 7

Motion sickness

• CP
• cause
• tx

Answer 7

CP: vertigo during passive motion during high likelihood of sensory mismatch (vision, vestibular, proprio mismatch)

cause: brain’s multisensory integration process FAILS to reconcile the discrepancy of inputs
tx: sx mgmt with vestibular suppressants (dimenhydrinate, meclizine)