Lying Down Nystagmus in Lateral Canal Paroxysmal Positional Vertigo

Aim: of this work is to deduce the position of the otoconial debris in lateral cupulo/canalolithiasis, as a function of two parameters: 1) the direction of the nystagmus that appears when the patient lies down (if present); 2) the positional nystagmus evoked by the supine roll test. The theoretical results are then compared with a population of 170 patients observed in the last ten years for vertigo due to paroxysmal positional vertigo of the horizontal canal. From the comparison between lying down and positional nystagmus, it is probably possible to identify the initial position of the fragments inside the lateral canal. This may be a useful clue for performing the correct liberatory maneuver. Instead, it is believed that to distinguish a jam located on the canal side of the cupula from a jam on the utricular side, one can only rely on the effective side of the liberatory maneuver. Background/Objectives: Aim of this work is to deduce the position of the otoconial debris in lateral cupulolithiasis or canalolithiasis based on two parameters: the direction of the nystagmus that appears when the patient lies down (if present) and the positional nystagmus evoked by the supine roll test. Methods: The theoretical results are then compared with a population of 170 patients observed in the last ten years for vertigo due to paroxysmal positional vertigo of the horizontal canal. Results: The study analyzed 170 cases of paroxysmal positional vertigo due to lateral canalolithiasis, comprising 141 geotropic and 29 apogeotropic forms. Among the geotropic cases, 80 showed no nystagmus in the supine position (GT0), 51 had supine nystagmus directed toward the healthy side (GT+, congruent), and 10 toward the affected side (GT−, incongruent). In the apogeotropic group, 10 had no supine nystagmus (AGT0), 16 exhibited nystagmus toward the affected side (AGT+, congruent), and only 1 toward the healthy side (AGT−, incongruent). Additionally, 2 cases showed monopositional apogeotropic nystagmus (mAGT), consistent with a “sieve-type” canal jam. Overall, 90 out of 170 patients (approximately 53%) had no nystagmus in the supine position: 80 out of 141 (≈57%) among geotropic forms and 10 out of 29 (≈34%) among apogeotropic forms. This difference was statistically significant (p = 0.0474, Yates correction), indicating that supine nystagmus is more frequent in geotropic than in apogeotropic variants. Conclusions: From the comparison between lying down and positional nystagmus, it is probably possible to identify the initial position of the fragments inside the lateral canal. This may be a useful clue for performing the correct liberatory maneuver. Instead, it is believed that to distinguish a jam located on the canal side of the cupula from a jam on the utricular side, one can only rely on the effective side of the liberatory maneuver.