Abnormalities of post-caloric nystagmus induced by postural change

Post-caloric nystagmus, the reverse secondary phase of caloric nystagmus after the cessation of primary-phase nystagmus, can easily be elicited by postural change. It has been related to the mechanism of vestibular adaptation, and exaggerated responses have been shown in some neurological disorders. Post-caloric nystagmus induced by postural change was analyzed in normal young adults (16 ears), elderly people (age > or = 65 years, 18 ears), patients with central lesions (40 ears) and patients with peripheral vestibulopathy (25 ears). The duration, maximum frequency and maximum slow-phase velocity of the primary phase of caloric nystagmus and of post-caloric nystagmus were documented. The duration, frequency and velocity ratios of post-caloric to primary-phase nystagmus were calculated. The results showed that post-caloric nystagmus induced by postural change was observed in 14 ears (88%) of normal young adults, 10 ears (56%) of elderly patients, 31 ears (78%) of patients with central lesions and 22 ears (88%) of patients with peripheral lesions. The duration and slow-phase velocity ratios for the central lesion group were found to be relatively higher than those for the control group (p < 0.05). A significant positive correlation between the intensities of post-caloric and primary-phase nystagmus was found in all groups except in the central lesion group. Abnormalities of post-caloric nystagmus induced by postural change may occur in the form of exaggerated response or failure of elicitation, which were observed with various central neuro-otological lesions and as a result of the aging process.