The direction of geotropic or ageotropic direction changing positional nystagmus in patients with lateral semicircular canal benign paroxysmal positional vertigo (LSC-BPPV) is reversed between the supine and prone positions. This reversal is also seen in other peripheral vestibular disorders. In this study, the positional nystagmus in the prone position was investigated in the patients with peripheral vestibular disorders except for BPPV. The positional nystagmus in the supine position was seen in 62 cases diagnosed as having peripheral vestibular disorders. They consisted of 33 with Ménière's disease (MD), 10 with sudden deafness (SD), 5 with vestibular neuritis (VN), 3 with Hunt syndrome (HS) and the remaining 11 cases with other lesions (OL). In these cases, the positional nystagmus in the prone position was investigated. When the direction of nystagmus was reversed in the prone position, it was defined as the reversal of nystagmus (RN). RN was seen in 27/33 MD (81.8%), 9/10 SD (90%) and 6/11 OL(54.5%). No RN was seen in VN and HS. In MD, SD and OL, all cases with canal paresis showed RN except 1 OL case. The cause of RN is suspected to be an inner ear disorder. Positional nystagmus in the prone position can assist in the diagnosis of peripheral vestibular disorders.
