Clinical Significance of Isolated Directional Preponderance of Caloric Nystagmus

Background and Aim: Bithermal caloric testing is a well-established testing modality in the evaluation of vestibular disorders. The main parameters calculated are unilateral canal weakness, directional preponderance (DP), and slow phase velocity. The aim of this study is to determine the clinical significance of isolated DP on bithermal caloric testing.

Material and Methods: Six patients (four men, two women) with a median age of 53.6 years (range, 35–69 years) presented in our neuro-otology department from January 2007 to December 2008. An isolated DP was defined as a DP of more than 40%(according to Jongkees formula) with less than 22% in unilateral weakness.

Results: All patients underwent thorough neuro-otologic evaluation, including pure tone audiogram (PTA), ABR, vestibular-evoked myogenic potentials (VEMPs), and videonystagmography (VNG), along with bithermal caloric testing. Diagnosis was set in all patients at the time of the caloric testing. Three of the patients were found to suffer from Ménière's disease (MD), two had benign paroxysmal positional vertigo (BPPV), and one had migrainous vertigo. Patients with BPPV underwent the Epley maneuver, MD patients were treated with salt deprivation and diuretics. and the migrainous vertigo patient was put on β-blockers prophylaxis. On follow-up, isolated DP was not recorded in the BPPV patients and in two of the MD patients.

Conclusion: An isolated DP on caloric testing is usually a transient, benign disorder. More than half of the patients with an isolated DP have either MD or BPPV.