The association of head shaking nystagmus with head-bending and lying-down nystagmus in horizontal canal benign paroxysmal positional vertigo.

Background: In benign paroxysmal positional vertigo (BPPV), the otolithic debris may alter the dynamics of the endolymph or cupula during head-shaking. This dynamic may generate head-shaking nystagmus (HSN) but exact pathomechanism of HSN in BPPV has not been elucidated. The association of positional nystagmus induced by head-bending or lying-down with HSN may help to understand the dynamics of HSN.
Objective: To assess the presence, pattern, and relationship with head-bending nystagmus (HBN) and lying-down nystagmus (LDN) of HSN in horizontal canal (HC)-BPPV.
Methods: We recruited 173 patients with HC-BPPV (76 geotropic and 97 apogeotropic). We analyzed the pattern of HSN, and correlation with HBN and LDN.
Results: Half of patients (83/173, 48%) with HC-BPPV showed HSN. The directional preponderance of HSN was also not found in patients with geotropic or apogeotropic HC BPPV (p = 0.488). The presence of HSN was related with the occurrence of HBN in both geotropic (p = 0.005) and apogeotropic type (p = 0.001). The direction of HSN was same with HBN and was opposite to LDN in both geotropic and apogeotropic type.
Conclusions: HSN was frequently found in patients with HC-BPPV and related with HBN and LDN. HSN in BPPV might be contributed by the otolith movements related with endolymph dynamics.