Lying-Down Nystagmus (LDN) – When a Lateralizing Sign of Secondary Importance Attains Ascendancy in the Diagnosis of Horizontal Semicircular Canal Benign Paroxysmal Positional Vertigo (HSC-BPPV)

BACKGROUND: The diagnosis of horizontal semicircular canal benign paroxysmal positional vertigo (HSC-BPPV) mainly depends on the elicitation of asymmetric horizontal positional nystagmus on rolling head to either side, during the diagnostic supine roll test (SRT). The asymmetry in the strength of the elicited horizontal positional nystagmus during SRT is explained by the Ewald's second law and is crucial for lateralizing the affected ear. Rarely the elicited horizontal positional nystagmus on the head roll to either side during the SRT is of symmetric strength. In such situations, the signs with secondary lateralizing value are useful in management by the repositioning maneuvers that require the affected side to be precisely known. AIM: The submitted article is a case report. RESULTS AND DISCUSSION: A 38-year-old male with two days history of vertigo on rolling to either of the lateral recumbent position was seen in the second week of March 2019. His SRT elicited a lying-down nystagmus (LDN) to the right, while the head roll to either side elicited a geotropic horizontal positional nystagmus of symmetric strength. The symmetrical strength of elicited positional nystagmus on SRT to either side led to ascendance of LDN from a lateralizing sign of secondary importance to one that reliably lateralized the involved horizontal semicircular canal. At two short term follow-ups at 1 hour and 24 hours after the therapeutic Gufoni maneuver, patient neither had vertigo nor any nystagmus elicited on the verifying supine roll test CONCLUSION: In rare instances, LDN, which is a lateralizing sign of secondary importance becomes pivotal in the management of HSC-BPPV especially when the affected side needs to be precisely determined for the execution of the therapeutic repositioning maneuver.