Diffential diagnosis of the caloric nystagmus

Diagnostic considerations based upon the nystagmogram are limited. Quantitative assessment of horizontal canal sensitivity is available through the use of culmination frequency or culmination slow phase velocity. Qualitative characteristics of nystagmometry have been sought but with no satisfactory results. Three distinctive features of the caloric nystagmus were evaluated and were found to be suggestive or outrightly pathognomonic for retrolabyrinthine or central nervous system abnormalities. These are: (1) Vestibular decruitment. The disproportionate caloric responsiveness when a weak stimulus elicits a more intense nystagmic reaction than a strong stimulus is capable of creating. (2) Hyperactive vestibular responsiveness (3) Ocular fixation reversal phenomenon. Contrary to the normal behaviour, the elimination of fixation decreases the nystagmus intensity instead of facilitating the evoked nystagmus. The assessment of these qualitative features of the caloric nystagmus in addition to the quantitative measurements widens the scope of our diagnostic capabilities.