ABSTRACT
Direction-changing nystagmus on positional testing is classically ascribed to a central pathology. We herein report a case of a patient with Benign Paroxysmal Positional Vertigo (BPPV) who demonstrated the unusual phenomenon of spontaneously reversing nystagmus, and discuss the theorised mechanisms with a novel illustration. In left lateral position, our patient's Videonystagmography (VNG) demonstrated an initially fast-phase geotropic nystagmus (leftward-beating, SPV 29°/s) which then paused for 8 s, then spontaneously reversed direction into a slow-phase ageotropic nystagmus (rightward-beating, SPV 7°/s). The rest of the neurootological examination and audiometry were normal. An MRI Brain scan also revealed no intracranial pathology. In subsequent reviews the vertigo resolved after repositioning manoeuvres for Left Horizontal Canal BPPV. With review of existing literature, this case may have exhibited coexistent left canalolithiasis and cupulolithiasis, resulting in simultaneous ampullopetal then ampullofugal forces in a single head position. Other posited theories include that of Endolymphatic Reflux and short-term central adaptation of the Vestibulo-Ocular Reflex. This case highlights a diagnostic challenge the otolaryngologists and neurologists may face with an atypical spontaneously reversing nystagmus in BPPV. However it remains a priority to rule out central pathologies first, and calls for specialists to take care in diagnosing horizontal canal BPPV by observing for a period of latency and spontaneous reversal of nystagmus first, so as to perform the appropriate repositioning manoeuvres. Laryngoscope, 2024.
