Patterns of low-frequency rotational responses in bilateral caloric weakness patients.

Analysis of low-frequency (0.01 to 0.16 Hz), sinusoidal rotary chair responses of 24 patients with bilateral caloric weakness revealed a wide range of vestibulo-ocular reflex (VOR) impairment. The rotational stimuli presented allowed characterization of the degree of VOR impairment from severe to no impairment even in patients with absent responses to ice water caloric irrigation. Five patterns of responses were described, which helps to explain the lack of correlation often seen between caloric and rotary chair test results, especially when rotational testing does not extend down to at least 0.02 Hz. Bilateral caloric weakness was confirmed in 79% and 71% of patients by test frequencies of 0.01 and 0.02 Hz. Rotational stimuli of 0.04, 0.08, and 0.16 Hz gave notably poorer performance with 54%, 50%, and 29% confirmation.