Clinical evaluation of the monothermal caloric test

The Torok Monothermal Caloric Test has been described as offering a strong advantage over bithermal caloric testing because it can distinguish labyrinthine from retrolabyrinthine lesions. Weak and strong irrigations of room-temperature water are administered to each ear and the ratios of strong to weak nystagmus responses compared to those of normal individuals. Ratios that fall below normal are said to represent decruitment and to denote retrolabyrinthine disease. Ratios that exceed normal are said to represent recruitment and to denote labyrinthine lesions. We attempted to verify the clinical value of the Monothermal Caloric Test by examining patients with known labyrinthine (N = 9) and retrolabyrinthine (N = 25) lesions. Ten patients with dysequilibrium and nonlocalizing testing were also examined. The test was performed exactly as described by the originator. Decruitment was found either unilaterally or bilaterally in 56% of patients with retrolabyrinthine lesions. However, it occurred on the side of the lesion in only 42%. Decruitment was also found in 47% of patients without retrolabyrinthine lesions, including 63% of those with unilateral Meniere's disease. Recruitment was never found on the side of a labyrinthine lesion. A description of the test and a summary of our results are presented. We conclude that the Monothermal Caloric Test is moderately sensitive to the presence of retrolabyrinthine lesions, but lateralizes poorly and is not highly selective. The test was found to be insensitive to the presence of labyrinthine disease.