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.