Lying down nystagmus in horizontal semicircular canal benign paroxysmal positional vertigo (HSC-BPPV)

Determining the lateralizing value of lying-down nystagmus (LDN) in horizontal semicircular canal benign paroxysmal positional vertigo (HSC-BPPV). The authors prospectively investigated LDN in 35 consecutive patients of HSC-BPPV (28 geotropic and 7 apogeotropic variants) attending an Otoneurology Centre in South Rajasthan India over a period of 20 months. LDN was present in 45.7% (16/35) patients of HSC-BPPV; 50% in those with geo-HSC-BPPV (14/28), and 28.6% (2/7) with apo-HSC-BPPV. When present, LDN directs contralaterally in 93% of geo-HSC-BPPV (13/14) and ipsilaterally in 100% of apo-HSC-BPPV (2/2). Only in 1 out of the 35 patients (2.9%), LDN was solitarily decisive in lateralizing the affected canal as the supine roll test elicited nystagmus of symmetric strength on the lateral head roll to either side. LDN is an important secondary sign of lateralization (SSL) in patients with HSC-BPPV (both geotropic and apogeotropic variants). LDN direction is mainly corroborative, but rarely when the lateral head rolls to either side elicits horizontal positional nystagmus of symmetric strength to either side, it can be solitarily relied on for lateralization.