Limits of normal for pressure sensitivity in the fistula test.

In patients with perilymphatic fistula (PLF), nystagmus may sometimes be elicited by application of pressure to the external ear canal. The extent to which the normal population also exhibits such 'pressure sensitivity' is presently unknown. Our goal was to determine the limits of normal pressure sensitivity and to quantify the performance of the fistula test. Our subjects consisted of 13 normal controls and 7 patients with a history of pressure sensitivity who later underwent exploratory tympanotomy. We measured nystagmus prior to and following pressurization of the external ear canal. Pressure was applied manually over 60 s with a pneumatic otoscope bulb. In normal subjects, change in nystagmus between prepressure and postpressure tests ranged from -1.3 to 0.9%s. In patients, change in nystagmus greater than the 95th percentile limits of normal was not a reliable indication of PLF.