Pseudo-spontaneous and head-shaking nystagmus in horizontal canal benign paroxysmal positional vertigo.

OBJECTIVES: To determine the characteristics and diagnostic value of pseudo-spontaneous and head-shaking nystagmus (HSN) in benign paroxysmal positional vertigo involving the horizontal semicircular canal (HC-BPPV).

STUDY DESIGN: Retrospective case series review.

METHODS: After excluding 19 patients with canal paresis, abnormal head impulse test, recent history of peripheral or central vestibular disorders, or poor cooperation, we retrospectively recruited 127 patients with HC-BPPV from January 2009 to July 2012. The patients included 69 geotropic and 58 apogeotropic types. We analyzed the pattern of pseudo-spontaneous nystagmus and HSN according to the lesion side.

RESULTS: Pseudo-spontaneous nystagmus was observed in 87 (87/127, 68.5%) patients, both in geotropic (46/69, 66.7%) and apogeotropic (41/58, 70.7%) types without difference in the prevalence between the types (p = 0.627). Pseudo-spontaneous nystagmus beat more to the lesion side in apogeotropic type (28/41, 68.3%, p = 0.028) but in either direction without directional preponderance in geotropic type (p = 0.659). Of the 90 patients who underwent horizontal head-shaking, 27 (30.0%) showed HSN that was more common in apogeotropic than in geotropic type (22/44 [50.0%] versus 5/46 [10.9%], p < 0.001). Patients with apogeotropic HC-BPPV showed predominantly contralesional HSN (19/22 [86.4%], p = 0.001), whereas patients with geotropic type did not show any directional preponderance of HSN (contralesional in 2 and ipsilesional in 3).

CONCLUSION: HSN is more common and mostly contralesional in apogeotropic HC-BPPV. HSN may be a lateralizing sign in apogeotropic HC-BPPV. Different prevalence and patterns of HSN in apogeotropic and geotropic HC-BPPV suggest dissimilar cupular dynamics in those disorders.