title: Reversal of initial positioning nystagmus in benign paroxysmal positional vertigo involving the horizontal canal.
abstract: In benign paroxysmal positional vertigo (BPPV), spontaneous reversal of the initial positioning nystagmus rarely occurs without further position changes. We analyzed the characteristics of spontaneous reversal of the initial head-turning nystagmus in 21 patients with BPPV involving the horizontal semicircular canal. All patients showed initial geotropic nystagmus (first-phase nystagmus) on head turning to either side while supine, which was followed by spontaneous reversal (second-phase nystagmus). The reversal was either unilateral (n = 16) or bilateral (n = 5). The maximal slow phase velocity (SPV) and duration of the first-phase nystagmus were greater and shorter than those of the second-phase nystagmus. The reversal group showed greater maximal SPVs of the initial nystagmus in either ipsi- or contralesional direction than the control group. BPPV resolved after particle repositioning maneuver (PRM) in most patients. However, one patient showed persistent apogeotropic nystagmus after PRM. Short-term adaptation of the vestibulo-ocular reflex seems to be the main mechanism of spontaneous reversal of the initial positioning nystagmus. However, coexistence of canalo- and cupulolithiasis should be considered in the patient showing bilateral spontaneous reversal.
authors: Department of Neurology, Chonnam National University Medical School, Gwangju, Korea.
authors: Seung-Han
authors: SH
authors: Lee
authors: Myeong-Kyu
authors: MK
authors: Kim
authors: Ki-Hyun
authors: KH
authors: Cho
authors: Ji Soo
authors: JS
authors: Kim
mesh_terms: D000222:Adaptation, Physiological; D000368:Aged; D004424:Ear Canal / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009759:Nystagmus, Pathologic / Q000503:physiopathology*; D012027:Reflex, Vestibulo-Ocular; D014717:Vertigo / Q000503:physiopathology*