LAUSR

Dear Editor-in-Chief, Downbeat nystagmus (DBN) is a common type of acquired nystagmus. Though it is generally attributed to central nervous system (CNS) diseases, mainly cerebellar dysfunctions or other posterior fossa abnormalities, it could be also idiopathic [1]. Recently, DBN has also been associated to peripheral vestibular pathologies. Benign paroxysmal positional vertigo (BPPV) involving the anterior semicircular canal [1] or the non-ampullary arm of the posterior semicircular canal (PSC) [2] has been assumed to elicit DBN in both Dix-Hallpike (DH) and/or straight head hanging (SHH) positions. In addition, spontaneous DBN has been described in other inner-ear dysfunctions such as inferior vestibular neuritis (IVN) and inferior labyrinth infarction [3]. The introduction of modern tools for vestibular testing, i.e., video-head impulse test (HIT) and vestibular-evoked myogenic potentials (VEMPs), has enabled a rapid assessment of the activity of ampullary and otolith receptors, respectively, and their afferents. A 41-year-old woman was admitted to the ENT unit for evaluation of positional vertigo without headache or auditory symptoms. She was initially seen in the emergency setting where a workup with bedside examination and braincomputed tomography (CT) scans excluded acute central pathology and a diagnosis of right PSC-BPPV was made. Three days of self-administered physical therapy at home led to worsening of symptoms with the onset of disabling dizziness. She referred recurrent migraine-related headaches in the past and two previous episodes of PSC-BPPV, both receded with appropriate canalith repositioning procedures (CRP). A spontaneous DBN with a torsional component in which the upper pole of the eyes beat toward the left ear could be detected on video-oculography (Online Resource 1). Nystagmus was suppressed by visual fixation, whereas it slightly increased after DH maneuvers on both sides and in SHH position. Bedside testing excluded oculomotor abnormalities, and both neurological examination and brain-magnetic resonance imaging (MRI) ruled out CNS involvement. Video-HIT (Fig. 1a) detected a selective right PSC-hypofunction, whereas cervical and ocular-VEMPs were bilaterally normal (Fig. 1b). A canalith jam (CJ) involving the non-ampullary arm of the right PSC was postulated (Fig. 2a) so the patient was submitted to Demi-Semont maneuvers [2] with mastoid vibrations. Symptoms promptly receded and video-oculography demonstrated an almost complete disappearance of both spontaneous and positional nystagmus after CRP (Online Resource 2). In addition, VOR-gain values in the plane of the right PSC normalized after CRP on video-HIT (Fig. 2b). BPPV represents the most common labyrinthine disorder and it is caused by inappropriate activation of semicircular canals ampullary receptors due to otoconial detachment from utricular macula. Debris can settle in different parts of the membranous ducts resulting in heterogeneous clinical features. Short-lasting vertigo spells triggered by quick headposition changes represent the most typical symptom [1]. PSC is considered the most commonly affected site due to its anatomically inferior location in both supine and upright positions. Typical PSC-BPPV due to otoliths settling on its ampullary arm is characterized by paroxysmal upbeat nystagmus with torsional components beating toward the undermost ear elicited by ipsilateral DH maneuver. Nystagmus results from excitatory activation of ipsilateral PSC-ampulla since debris move away from the cupula during diagnostic maneuvers [1]. A new variant of PSC-BPPV due to debris located in its non-ampullary arm has recently been described, with Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10072-020-04529-9) contains supplementary material, which is available to authorized users.