Efficacy of the Fixation Index of Bithermal Caloric Test for Differentiating Brain Lesions in Vestibular Disoder

Objectives: This study was performed to investigate the efficacy of the fixation index (FI) of the bithermal caloric test for differentiating brain lesions in vestibular disorder.Methods: We reviewed the medical records of 286 consecutive dizzy patients who underwent brain magnetic resonance imaging (MRI) and the bithermal caloric test at department of otorhinolarnygology. Central vestibulopathy (CVP) was defined as when corresponding lesion was identified on brain MRI, otherwise peripheral vestibulopathy (PVP) was defined. The FI was defined as the mean slow phase velocity (SPV) with fixation divided by the mean SPV without fixation, and failure was indicated when the FI exceeded 70%.Results: The CVP confirmed by brain MRI and PVP were 16.8% and 83.2%, respectively. The most common CVPs were cerebellopontine angle tumor (n=19, 39.6%) and chronic cerebellar infarction (n=18, 37.5%). There were 23 cases of CVP (47.9%) and 47 cases of PVP (19.7%) with abnormal number of FI in at least two of the four caloric irrigations. The FI score of right cool (RC), left cool (LC), and right warm (RW) were also increased significantly in patients with CVP (p=0.031 at RCFI, p=0.014 at LCFI, p=0.047 at RWFI, and p=0.057 at LWFI; Mann-Whitney U-test).Conclusions: If two or more abnormal FIs are detected during bithermal caloric testing, there is a high likelihood of CVP. Consequently, additional brain MRI may be necessary for further evaluation.