Primary symptoms of acute vestibular impairment

What are the primary symptoms of acute vestibular impairment? 

The Committee for Classification of Vestibular Disorders of the Barany Society published the vestibular symptom classification scheme in 2009.

Vestibular symptoms can include vestibulo-ocular, vestibulo-spinal, and vestibulo-autonomic symptoms and may include disequilibrium, vertigo, oscillopsia, nausea, nystagmus, diaphoresis, increased heart rate, and respiration.

Disequilibrium, or poor balance, is caused by the decrease in signal to the vestibulo-spinal tracts.

Vertigo, the illusion of self-motion, may be perceived as angular (spinning, whirling, or gentle rocking) or linear (to and fro, side to side).

Vertigo is probably caused by decreased signals to the vestibular cortex. Oscillopsia, a related sensation, is the illusion of motion in the visual world around the individual and is probably caused by nystagmus.

The primary characteristics of the symptom history include symptom onset and duration, time course (constant or episodic), specific triggers and other aggravating or alleviating factors, associated symptoms, and family history of similar episodes.

International Classification of Vestibular Disorders I (ICVD-I) Classification of Symptoms v1.0 (January 2009)

• 1. Vertigo
  • • Spontaneous vertigo
  • • Triggered vertigo
    • • Positional vertigo
    • • Head-motion vertigo
    • • Visually-induced vertigo
    • • Sound-induced vertigo
    • • Valsalva-induced vertigo
    • • Orthostatic vertigo
    • • Other triggered vertigo
• 2. Dizziness
  • • Spontaneous dizziness
  • • Triggered dizziness
    • • Positional dizziness
    • • Head-motion dizziness
    • • Visually-induced dizziness
    • • Sound-induced dizziness
    • • Valsalva-induced dizziness
    • • Orthostatic dizziness
    • • Other triggered dizziness
• 3. Vestibulo-visual symptoms
  • • External vertigo
  • • Oscillopsia
  • • Visual lag
  • • Visual tilt
  • • Movement-induced blur
• 4. Postural symptoms
  • • Unsteadiness
  • • Directional pulsion
  • • Balance-related near fall
  • • Balance-related fall

Nystagmus is the rapid, involuntary, back-and-forth motion of the eyes. In the acute period quick phases beating away from the involved side alternate with slow phases moving toward that side, usually horizontal with a torsional component.

The nystagmus has greater amplitude when vision is absent (prevents the ability to fixate visually), such as when the patient is tested with Frenzel lenses or infrared video oculography (VOG).

In peripheral lesions the nystagmus is more intense when the patient looks toward the direction of the quick phases, i.e., away from the involved side; this phenomenon is known as Alexander’s law . Alexander’s law is not usually true of central lesions. 

The patient has oscillopsia because higher centers, which have not given movement commands, do not expect visual feedback from movements of the eyes.

When the individual makes a movement that the brain has planned, theoretically the brain plans to expect certain sensory feedback arising from that movement and a copy of the motor command may be sent elsewhere in the brain to await that feedback. (The copy is known as efference copy or corollary discharge .

If the expected feedback is received after the movement the individual knows that he has moved and can use that feedback to determine if the movement was successful or if the motor command should be adjusted on the next trial. If the movement was not successful the individual can use the feedback to adjust the motor command on the next trial.

This movement–feedback loop is the theoretical basis for motor learning.) In an individual who has a vestibular disorder and whose subcortical oculomotor system is generating nystagmus, no efference copy will be received by some higher center in expectation of receiving visual feedback.

Therefore, the motion of the visual image across the retina will be misinterpreted as motion of the world around the person rather than motion of the eyes and, therefore, the patient will experience oscillopsia. 

Patients may have nausea, diaphoresis, and cardiovascular signs because of vestibulo-autonomic projections of the vestibular nuclei to several nuclei such as the parabrachial nucleus, nucleus of the solitary tract, nucleus ambiguous, and dorsal nucleus of the vagus nerve.

Sources

From Bisdorff A, von Brevern M, Lempert T, Newman-Toker DE: Classification of vestibular symptoms: towards an international classification of vestibular disorders, J Vestib Res 19(1-2):1-13, 2009.