OBJECTIVETo investigate the manifestation of head shaking nystagmus (HSN) and the relationship between HSN and vestibular bithermal test while cross-checking the HSN and vestibular bithermal test.

METHODSOne hundred and twenty-four patients were examined by HSN and vestibular bithermal test. The latency and duration of HSN were observed and the dynamic changes of HSN were also investigated. The results of bithermal test were clarified by the values of canal paresis (CP).

RESULTSThere were 3 types of HSN, including 41 monophasic HSN, 11 biphasic HSN and 7 perverted HSN. The latency of monophasic HSN was (2.75 +/- 1.41) ms and the duration of it was (32.16 +/- 20.30) ms; as for the biphasic HSN, the first phase had no latency and the duration was (12.33 +/- 4.42) ms which was shorter than that of the second phase (57.00 +/- 17.19) ms (P < 0.01) and the latency of second phase was (57.00 +/- 17.19) ms. The value of canal paresis in the patients without HSN was lower than that in the patients with HSN.

CONCLUSIONSThe existence of HSN was dependent on the loss of the function horizontal canal and also on the stage of vestibular compensation. The variation of duration of HSN among individuals was great. In the acute stage of unilateral vestibular function loss, there appeared to be prominent HSN, and the direction of HSN is the same as that of spontaneous nystagmus. With the development of vestibular compensation, biphasic nystagmus would appear instead of monophasic HSN and the direction of first phase represent the direction of un-lesioned side. After compensation, HSN would not be elicited. However,when HSN existed, it suggested that the value of CP should exceed 25%. Perverted nystagmus pointed to central abnormality.