Post caloric nystagmus: an analysis of culmination frequency and maximum slow phase velocity

Neurons of the vestibular nuclei receive substantial afferent inputs from various parts of the cerebellum and brainstem. The efferent output of the vestibular nuclei thus reflects the interaction of these connections. This study investigates the influence of lesions of the posterior neuro-axis (PNA) on thermally induced nystagmus in 70 such patients. The caloric responses of all these patients were analyzed automatically with respect to culmination frequency (CF), but an automated analysis of SPVMax was possible in only 36 of these patients. Analysis of both sets of data showed that the coefficient of variation of SPVMax was significantly greater than that of CF. Vestibular decruitment, which correlates well with PNA lesions, was noted in 83% of cases when CF was used. In contrast, when SPVMax was used, vestibular decruitment was noted in only 53% of patients. Considering the low coefficient of variation of CF and considering that vestibular decruitment is noted with greater reliability when this variable is used, it is recommended that caloric nystagmus should be analyzed with respect to frequency rather than SPVMax.