Neuroscience 10 Dizziness and Vertigo



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Neuroscience 10 – Dizziness and Vertigo

Anil Chopra
Vertigo (illusory movement) is a special case of a more general set of symptoms ‘Spatial Disorientation’. It may be caused by anything which disrupts the normal transactions between the organism and environment, either functional or structural and at a peripheral or central level of organisation.
Disabling dizziness is experienced by 70% of the population at some point in their life and is normally handicapping.
Taking a History

  • Patients often find it difficult to describe what “dizziness” is.

  • Anything which affects normal interaction with the world can result in disorientation and illusory movement.

  • Marked vertigo with nausea is a sign on peripheral vascular disorder.

  • Symptoms include

    • Intense spinning (rotational vertigo)

    • Nausea

    • Patient feels as if they are on a boat

    • Patient feels as if the ground is unsteady

    • Patient feels as if the world is spinning due to vestibular nystagmus.



Vestibular Disorder

Can be functional or structural:



Structural: caused by

  • irritative disease

  • destructive disease


Functional: caused by

  • misinterpretation of sensory input by the brain

  • mal adaptation

  • loss of rules of correspondence between senses

  • over awareness/magnification of sensory input

Can be both i.e. a structural disease which leads to chronic dysfunction.



  • The general rule is that if the head is moved in a particular direction, the semi-circular canal in that plane on that side will increase its rate of firing i.e. if the head is turned to the right, then the right canals are stimulated.

  • When the head is still the semicircular canals have an equal tonic firing rate.

  • If there is a problem (e.g. lesion) in the left side, then the right side will signal unopposed action potentials to the brainstem. This will give the patient the feeling as if they are turning right which cause vertigo.

  • It also has an effect on the vestibulo ocular reflex. The slow drift will be to the left and the fast saccade to the right causing vestibular nystagmus.

  • Similarly if there is irritatory excitation on a particular side, then the patient will have the illusory feeling of rotating toward that side.


Treatment of common vestibular disorders:

    • Reassurance that the patient is understood

    • Pharmaco treatment – anti-virals, anti-emetics

    • Treat associated anxiety, depression

    • Cognitive behaviour therapy with desensitisation and physiotherapy

    • Behavioural axiolytic tactics

    • Minimise risk factors

Causes of Vertigo



Duration

Cause

Seconds

Benign Paroxysmal Positional Vertigo (BPPV) – this is caused by a build up of debris in the semi-circular canals.

Minutes


Vertebrobasilar insufficiency (insufficient blood going to the brain via vertebral and basilar arteries), migraine.

Hours

Meniere’s syndrome (disorder of the inner ear),

Days

Vestibular neuritis, infarction of labyrinth, herpes.

Continuous

Vestibular lesion

Mechanisms of common types of dizziness


Type Mechanism


Vertigo Imbalance in tonic vestibular signals

Near-faint dizziness Diffuse cerebral ischemia

Psychophysiologic Impaired central integration of sensory signals

Hypoglycemic dizziness Inadequate brain glucose; increased circulatory catecholamines

Disequilibrium Loss of vestibulospinal, proprioceptive, cerebellar, or motor function

Ocular dizziness Visual-vestibular mismatch due to impaired vision

Multisensory dizziness Partial loss of multi sensory system function

Physiologic Sensory conflict due to unusual combination of sensory signals

Drug-induced dizziness CNS agents; change in cupula’s specific gravity (alcohol).
Vestibular Neuritis

“Acute Unilateral Vestibular Disorder”

Symptoms:


  • vertigo

  • oscillopsia (objects appear to be vibrating)

  • imbalance

  • nausea

  • vomiting

  • quick onset

  • nystagmus

  • pallor (pale)

  • obvious ataxia (in-coordination of muscle movements)

These symptoms are intense for 1 or 2 days and then recover in a week or so.
Treatment:

  • steroids

  • anti-viral (cyclovirs)

  • anti emetic

Disorders of Hearing



Conductive losses:

  • Wax in the external meatus and middle ear otitis

  • Otosclerosis

  • ossicular discontinuity

  • tympanic rupture

  • congenital

  • Cholesteotoma


Sensory (cochlear losses)

  • Presbyacusis and noise exposure

  • Inherited and secondary degenerations

  • Ototoxicity

  • Fistula (morphological disorders affecting cochlea)

  • Hydrops (Menieres disease and secondary)

  • Congenital


Neural (VIIIth nerve)

  • Acoustic neuroma

  • Demyelination

  • Herpes

  • Neural hearing loss (uncertain origin)


Spatial Orientation

People have awareness of spatial orientation using:



  • Vision: disorders here can result in the railway carriage illusion; visual vertigo; oscillopsia.

  • Hapatic senses: i.e. touch, vibration, e.t.c. disorders here can result in plastic rubbery legs and undulating floor

  • Vestibular signals: Provide a spatial reference for other senses. Disorder here can result in vertigo; motion sickness; derealisation.

Examinations of Hearing and Balance
Testing the integrity of the vestibular system can be useful to assess the condition of the brainstem, especially in comatosed patients.
Eye Movements

Caloric Test

  • Have the patient lying at a 30º angle.

  • Inject either hot or cold air into their ear.

  • With hot air, the convection currents cause endolymph to move and thus stimulating excitation from the ampulla. The eyes will move contra-laterally (in the opposite direction) to the injected ear.

  • With cold air, the convection currents cause endolymph move in the opposite direction, stimulating inhibition from the ampulla. The eyes will move ipsilaterally (in the same direction) to the injected ear.

  • Small amplitude short duration response to both hot and cold on one side à canal paresis (loss of movement in the semicircular canals).

  • Bilateral small short responses à bilateral hypofunction.

  • Asymmetry of hot/cold responses is of little significance.


Head Rotation Test

  • Ask the patient to stay focused on the doctor’s eye, and rotate their head.

  • Normal response will be that the eyes stay focused.

  • In vestibular dysfunction, the eyes will go with the head and not keep fixation and patients often make saccades back to the fixation point. The lesion is on the side of rotation.


Balance

  • Patients will sway when standing still if they have vestibular dysfunction.

  • They may also lean to one side or have a head tilt (lesion).

  • Patients may also veer to one side when attempting to walk. (unilateral loss)

  • Patients find it difficult to walk in the dark. (bilateral loss).

  • Ask patient to walk briskly turning rapidly to right and left. Observe impairments, particularly asymmetry.


Hearing

  • A tuning fork at 512Hz is needed.


Rinne tests

Place the fork over the meatus of a normal ear will sound slightly louder than placed on the mastoid. With a conductive loss the fork is louder on the mastoid.


Weber test

Test for sensor-neural hearing independent of conductive attenuation.



When the fork is placed on the mid-forehead the tone is normally heard ‘in the middle of the head’. If there is a sensory loss on one side the tone is localised to the good side.


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