Significance of Correcting the Spontaneous Nystagmus in Siusoidal Harmonic Acceleration Test

Lee, Hyun Jung; Jung, Sung Do; Jung, Jae Yun; Suh, Myung Whan

Abstract

BACKGROUND AND OBJECTIVES
Spontaneous nystagmus may have an influence on the results of sinusoidal harmonic acceleration (SHA) test, although it has not been ascertained through sufficient studies. This study evaluated the effect of spontaneous nystagmus on the gain, asymmetry and phase values of the SHA test.
SUBJECTS AND METHOD
We retrospectively analyzed 19 patients with acute unilateral vestibular weakness and spontaneous nystagmus (sn). All patients underwent a battery of vestibular testing including videonystagmography, bithermal caloric test, and SHA test. Gain, asymmetry, and phase were calculated with the conventional method without correcting for sn, thus the non-corrected SHA (nSHA). Then the same three parameters were calculated again after manually correcting for spontaneous nystagmus, thus the corrected SHA (cSHA). The two methods were compared with respect to gain, asymmetry and phase values. Correlation between the SHA test and caloric test was also analyzed.
RESULTS
The gain of nSHA was significantly larger than that of cSHA in all frequencies. There was no difference in the phase values between the two analysis methods. The asymmetry of nSHA was 2.8 times larger than that of cSHA. The asymmetry values of both nSHA and cSHA showed a significant correlation between the caloric test and degree of spontaneous nystagmus.
CONCLUSION
It seems that the SHA test is significantly influenced by spontaneous nystagmus. Although correcting for spontaneous nystagmus may not always be necessary, we should consider the effect of spontaneous nystagmus when interpreting the SHA test results of a patient who has spontaneous nystagmus.