Diagnostic value of velocity-step responses.

For the nystagmic (after-)response in each direction it was evaluated in 618 patients whether the gain (initial velocity) and the time constant were normal, significantly low or high, thus constituting a specific 'response pattern'. In a number of diagnostic categories, 65% of the response patterns were 'typical', i.e., they were found in significantly high frequency. Symmetrical response patterns were predominant. Short time constant(s) and/or low gain values in either or both directions were found in labyrinthine defects. High gain values were found in otosclerosis after footplate surgery, in multiple sclerosis, hyperventilation syndrome, posterior fossa tumour and spasmodic torticollis. In those categories, except otosclerosis and posterior fossa tumour, also significantly high values of the time constant were found, as well as in the category of patients with exposed tympanic cavity and dizziness. A significant directional preponderance indicating the defective side was found for the low-frequency gain (i.e., the product of initial velocity and time constant) in 48% of the patients with unilateral canal paralysis. It is concluded that the velocity-step test is a powerful diagnostic tool in vestibular examination.