Pseudocaloric nystagmus.

Pseudocaloric nystagmus (PCN) is an appropriately beating nystagmus induced by cold caloric irrigation of an ear with abolished vestibular function. The nystagmus is not the result of endolymph flow but probably represents unmasking a latent nystagmus by altering the patient in this case, through tactile (caloric) stimulation. Pseudocaloric nystagmus has the following characteristics: (1) mild intensity (eyes closed-slow phase velocity usually less than 8 degrees/sec), it has not been observed with the eyes open, (2) always beats away from the diseased ear; therefore, any nystagmus induced by cold irrigation will be appropriately (contralateral) beating while that induced by warm irrigation will be inappropriately (contralateral beating; 3) the induced nystagmus will not reverse direction after inverting the ampulla. Establishing bidirectional sensitivity of the cupula by demonstrating appropriately beating nystagmus to ampullopetal and ampullofugal flow of endolymph not only assures that the lateral semicircular canal (SCC) is functionally intact to caloric stimulation but will avoid errors in electronystagmorgraphic (ENG) interpretation.