The Hearing and Equilibrium Committe of The American Academy of Otolaryngology–Head and Neck Surgery (AAO–HNS) recommended a definition that states “vertigo is the sensation of motion when no motion is occurring relative to earth’s gravity.”
True vertigo is defined as “a false sense of motion”: either you are moving or the world is moving about you. Whirling vertigo is a “special case” of vertigo just as a square is a special case of rectangles. Although rotatory or whirling vertigo is often caused by the inner ear, the ear can cause other movement sensations and the central nervous system can cause rotatory sensations. Patients with true vertigo need an otologic work-up. Psychogenic dizziness is a difficult issue. Most often, patients describe a “spacey” or “disconnected” dizziness without any feeling of motion or loss of balance. Dizzy patients are often anxious or depressed or belligerent, and these feelings may so dominate their behavioral style that the physician cannot see past them to the balance disorder.
Acute inner ear pathology typically causes a spinning sensation. For this reason, dizziness that is described as a sensation of spinning or turning strongly indicates that the cause is an inner ear disturbance. Inner ear disorders do not always cause spinning. If inner ear disorders are mild or if compensation reduces the severity of the symptom, words like “imbalance, drunkenness, wooziness, swaying, floating, fainting” or others may best describe the sensation. Under this definition any type of motion—spinning, veering, swaying, bobbing, or other—qualifies as vertigo.
The assessment of vestibular function is generally based on the study of the vestibulo-ocular reflex (VOR) elicited in the caloric and rotatory chair tests. In these tests, the characteristics of nystagmus are specific and can be predicted because the stimulus most directly effects the receptors in the horizontal semicircular canal (HSC). Several different techniques are available to study the VOR, but the bithermal alternating water irrigation paradigm (caloric) and the single sinusoidal test at multiple frequencies (sinusoidal harmonic acceleration [SHA]) along the yaw axis (rotatory chair) are those most frequently used. The most widespread techniques to record and analyze the results of these tests are electronystagmography and videonystagmography.
The bithermal caloric test is performed according to Fitzgerald and Hallpike. Each ear is irrigated alternatively with a constant flow of water at 30 C and 44 C for 40 seconds. The response is recorded over 3 minutes, and a 7-minute interval between each stimulus is respected to avoid cumulative effects.
The rotatory chair is housed in an enclosure to perform the test in the dark, and the head is restrained and positioned so that both HSCs are close to the plane of stimulus (at the gravitational horizontal). Alertness was maintained. Eye movements are recorded by electrooculography with electrodes conveniently placed to register horizontal nystagmus.
Computerized Dynamic Posturography
In this test, the patients are asked to maintain their balance under 6 different conditions. The first 3 conditions (SOT 1, SOT 2, and SOT 3) provided accurate uninterrupted foot support surface information. The visual information provided is different in each of the 3 conditions. In SOT 1, the patients remain with their eyes open, and in SOT 2, they have their eyes closed. In SOT 3, the patients remain with their eyes open but the surroundings move in a pattern stimulated by the anteroposterior swaying movements that he or she continuously performs. In conditions SOT 4, SOT 5, and SOT 6, the visual scenario corresponds to that described for SOT 1, 2, and 3, respectively, but in each, the anteroposterior sway movement of the patient drives the movement of the supporting surface in an axis parallel to the ankle joint. For each SOT condition, several trials are performed; in each, the anteroposterior sway is measured and a value is calculated relative to a sway of 12.5 degrees, which is considered the maximum anteroposterior sway about the ankle joint in normal subjects.