Dizziness and Deafness

Taha Gholipour

Stephen W. Parker

Vestibular system: Otolith organ cilia are floating w/in endolymph (viscous fluid). Mvmt of head causes endolymph to move in opp direction. Direction of mvmt is encoded by one or more otolith organs; amplitude is encoded by firing rate of the cilia (proportional to degree of bending). Otolith organs sense linear (saccule & utricle) & rotational (semicircular canals) acceleration.

Auditory system: Sound → vibrates basilar membrane of organ of Corti thru TM → middle ear ossicles → fluid wave of endolymph in cochlea.→ Hair cells signal transmitted thru cochlear/auditory nerve to dorsal + ventral cochlear nuclei → superior olivary n. → inferior colliculus. → medical geniculate n. → auditory cortex (transverse temporal gyri of Heschl).

APPROACH TO DIAGNOSIS OF DIZZINESS

Must be cautious interpreting history as per nature of the condition; pt’s description & word selection might not be helpful in localizing the abnormality. Exam findings in central lesions can sometime mimic peripheral etiologies & misleading if not interpreted in context.

History: Key questions: meaning of “dizzy,” (room spinning, light-headedness, giddiness, imbalance), pace of sx very useful (acute, subacute, chronic, episodic), positional vs. constant, assoc sxs (visual changes, hearing loss, weakness), previous h/o similar sxs, meds (&Dgr;s or new additions). Pt’s PMH, FH, or risk factors for cerebrovascular disease, malignancy, or inflammatory or infectious causes can guide exam & imaging.

Elements of History: Central vs. Peripheral Features^a
	Central	Peripheral
Nausea	Variable	Variable
Positional	Rare	Common
Diplopia, dysarthria, dysphagia	Common	Rare
Imbalance	Variable, often severe	Variable, often mild/moderate
Hearing loss, tinnitus	Rare	Common
Oscillopsia	Severe	Mild
Other neurologic sx	Common	Rare
Recovery	Months	Days-weeks
Recurrence	Rare	Variable
^aClassic features—central lesions can mimic peripheral features.

Sxs	Mechanism
Disequilibrium: Imbalance or unsteadiness while standing or walking	Multiple: loss of vestibulospinal, proprioception, visual, motor fxn, joint pain/instability, & psych factors
Light-headedness or presyncope	Decreased blood flow to the brain
Sense of rocking or swaying as if on a ship (mal de debarquement)	Vestib syst adapts to continuous passive motion, must readapt once envir stable. Anxiety.
Motion sickness	Visual-vestibular mismatch
N & V	Stimulation of medulla
Oscillopsia: Illusion of visual motion	Spontaneous: Acquired nystagmus head induced: Severe, b/l loss of the VOR
Floating, swimming, rocking, & spinning inside of head (psychologically induced)	Anxiety, depression, & somatoform d/os
Vertical diplopia	Skew deviation
Vertigo: rotation, linear movement, or tilt	Imbalance of tonic neural activity to vestib system

Physical examination: Key elements: Orthostatic vital signs, general exam, visual acuity, eye movements (spontaneous, pursuit, saccades), looking for long tract sensorimotor deficits or signs (weakness, Horner’s, loss of pinprick OR touch sensation, Babinski’s), vestibular-ocular reflex testing, position testing, axial & appendicular coordination (e.g., finger mirroring and heel-to-shin for appendicular), stance & gait (never defer).

Exam findings: Central vs. Peripheral features^a
	Central	Peripheral
Neurologic signs: CNs, weakness, sensory &Dgr;, dysmetria, ataxia	Common	Rare
Nystagmus^b	Pure vertical or torsional, multidirectional, can change direction w/gaze, dysconjugate, no suppression w/fixation	Torsional and/or horizontal, unidirectional in all gazes, conjugate, suppresses w/fixation
Head impulse, thrust^b	Maintains fixation	Impaired fixation w/catch-up saccade
Alternate cover test^b	Skew deviation, vertical ocular misalignment apparent in alternate fixation	No vertical jump w/alternate refixation
Caloric test	Poor fixation suppression	Canal paresis
^aClassic features—central lesions can mimic peripheral features. ^bThree-step exam of head impulse, nystagmus, Test of Skew (w/the mnemonic HINTS) is shown to be sensitive & specific for detecting central causes of acute vestibular syndrome such as stroke from peripheral causes (see Stroke 2009;40:3504-3510).

Vestibular-Ocular Reflex Testing
Test	Procedure	Result
Vestibular dynamic visual acuity	Static, distant visual acuity is determined w/the head still. Dynamic visual acuity determined while pt’s head oscillated manually at 2 Hz.	A dynamic visual acuity of three or more lines above static visual acuity indicates a vestibular defect.
Head thrust	Pts fixate on a visual target, & eye position is observed immediately after a small thrust of the head to the left & right.	A refixation saccade & oscillopsia after head thrust toward dysfxnal canal indicates impaired VOR.
Head-shaking nystagmus	Pitch the pt’s head down 30 degrees & oscillate the head horizontally 20×.	Elicitation of jerk nystagmus after head shaking indicates a vestibular imbalance.