Vertigo, dizziness and balance disorders
Dizziness is a common reason for patients to consult a doctor. The dizziness may stem from a stroke but is usually the sign of an inner ear problem. It is essential for the patient to specify the type of dizziness experienced: does the room spin or does the patient feel unsteady, have balance problems, or a feeling of drunkenness? Are these sensations accompanied by auditory signs (feeling of blocked ears or tinnitus)? Are they accompanied by nausea and/or vomiting? And lastly, do they occur when the patient moves his or her head?
Over the last decade, there has been substantial progress in rotary vertigo testing. It involves assessing the functioning of the five inner ear receptors (or peripheral vestibular system). Any rotary vertigo or balance disorder requires otoneurological testing by a leading specialist, with the appropriate apparatus. These apparatus will help to diagnose the specific cause of the dizziness and clarify the imaging results (CT Scan, brain MRI) to start the patient on the most suitable treatment.
The peripheral vestibular system is made up of five different types of sensors in each ear: three semi-circular canals (horizontal, and anterior and posterior vertical canals) and two otolithic organs (the utricle and the saccule), i.e. a total of ten receptors. They send information to the central nervous system via the vestibular nerve made up of two parts: the superior vestibular nerve, comprised of the anterior and horizontal canal nerves and the inferior vestibular nerve comprised of the posterior canal and saccular nerve.
The clinical examination serves to detect the presence of an ocular nystagmus, evidence of vestibular asymmetry, to specify whether it is horizontal or vertical, and to detect a torsional component. Ocular nystagmus is comprised of slow eye movements with rapid intermittent phases in the opposite direction.
For diagnosis, the patient must be sitting and lying down with a videonystagmoscopy mask, placing the patient in the dark to prevent inhibition by fixation (Figure 1). This mask is equipped with a camera and monochrome infrared lighting, and involves detecting the iris imprint. A 3D study  of the components of the spontaneous nystagmus is essential. Ocular nystagmus is diagnosed when the patient is sitting and lying down and after different kinds of stimulation (head shaking test, vibration test, head impulse test).
Described for the first time by Bárány, these tests serve to assess the sensitivity of the ampullae of the horizontal semicircular canals. They mainly test the labyrinth and remain a key examination in studying how well the ampulla of the horizontal semicircular canal functions. What is more, contrary to the aforementioned tests, caloric tests have a quantitative value. They also serve to specify the sensation perceived, which is one way of demonstrating how the vestibular information is incorporated centrally. In practice, each ear is irrigated, either with cold water (30°C), or warm water (44°C) for 30 seconds, and the response is recorded between the 60th and 90th second after the start of stimulation. This test serves to assess how well the horizontal vestibule-ocular reflex functions on low frequency bands of around 1/1,000 Hz.
Subjective horizontal and vertical perception test
This test serves to assess how well the otolithic system functions. It consists in asking the patient, in the dark, to position a 60 to 90 cm luminescent bar placed 1m in front of him and at a 45° tilt, in a position that he believes is either vertical or horizontal. When there is an acute unilateral problem with the otolithic receptors, the patient places the bar in a position that is off-horizontal or off-vertical by around 3 to 10° on the damaged side.
Cervical evoked myogenic potentials induced by intense sound stimuli in the sternocleidomastoid muscles (or saccular-induced otolithic evoked potentials)
Clicking sounds or short tone bursts of 100 dB are delivered on one side using a helmet with a frequency of 5 Hz and cervical myogenic evoked potentials are collected in both sternocleidomastoid (SCM) muscles using surface electrodes placed on the upper third of these two muscles. The early waves are comprised of a first positive wave after 10 ms (P13 wave) followed by a negative wave after 19 ms (N23 wave). These waves show that a labyrinth receptor, the saccule, and the saccular nerve function.
Ocular evoked myogenic potentials induced by intense sound stimuli (or utricular-induced otolithic evoked potentials)
Intense sounds are delivered in each ear and the evoked potentials are collected using surface electrodes on the extraocular motor muscles on the opposite side (n1-p1 waves). This new test serves to assess the functioning of the utricle and utricular nerve, comprising the superior vestibular nerve.
Testing for balance disorders
Balance disorders (feeling of drunkenness, unsteadiness, tipping) are common with vestibular problems. They can be quantified with the help of fixed or mobile platforms using static and dynamic posturography methods.
This apparatus is used to test the patient’s static and dynamic balance. It includes two main types of tests: one sensory organisation test and one motor control test.
The sensory organisation test verifies the effect of six different sensory environments on postural control. To this end, the EquiTest includes a force plate that is fixed or that follows the movements in the patient’s centre of gravity, and a visual panorama placed 50 cm from the patient, which may be fixed or follow the movements in the patient’s centre of gravity. The EquiTest is a precious tool to help appreciate and quantify balance problems. To a certain extent, it also helps to guide vestibular rehabilitation and to assess its effectiveness.