Head Position Dependency of Induced Nystagmus to Ice Water Irrigation in peripheral vestibulopathy

ABSTRACT

BACKGROUNDS AND OBJECTIVES: The direction of caloric nystagmus depends on the head position as long as vestibular function is remaining but the it does not depend on head position change in the lateral semicircular canal (SCC) plugged ear, which is attributed to thermoconvection in the lateral SCC. So determination of head position dependency using ice water test is recommended in the evaluation of peripheral vestibulopathy in which dead labyrinth is suspected. Since ice water test in prone position is frequently skipped and neglected in many vestibular laboratories, we investigated the importance and necessity of evaluating head position dependency for the candidates of ice water test and estimated the amount of head position non-dependent component in discussion. MATERIALS AND METHOD: From January through September 2003, 25 patients, who showed no nystagmus during warm irrigation, were included in this study. Following forty milliliter of ice water irrigation in supine & prone position, the maximum slow phase eye velocity (SPEV) and direction of nystagmus were assessed using video nystagmography system. RESULT: Eleven cases showed head-position dependency and were interpreted as hypofunction of lateral SCC. Fourteen cases did not show head position dependency suggesting the absence of end organ function. However, in the latter group, 6 patients, who showed definite nystagmus to ice water irrigation in supine position, can be midinterpreted as hypofunction if ice water test in prone position is not performed. CONCLUSION: Evaluation of head position dependency in ice water irrigation is an important procedure in the determination of lateral SCC function and can provide valuable information when vestibular ablative procedures are considered.