Persistent Down-Beating Torsional Positional Nystagmus: Posterior Semicircular Canal Light Cupula?

Abstract

A 16-year-old boy with rotatory positional vertigo and nausea, particularly when lying down, visited our clinic. Initially, we observed vertical/torsional (downward/leftward) nystagmus in the supine position, and it did not diminish. In the sitting position, nystagmus was not provoked. Neurological examinations were normal. We speculated that persistent torsional down-beating nystagmus was caused by the light cupula of the posterior semicircular canal. This case provides novel insights into the light cupula pathophysiology.

Less common forms of posterior canal benign paroxysmal positional vertigo

“…Epley 16 considered atypical all forms of positional vertigo whose evoked nystagmus did not respect the usual patterns. Rarer variants of posterior canal BPPV do exist and are sustained by various clinical observations [2][3][4][5][6][7][8][9][10][11][12][13] . They are explained either by anomalous localisation of otoconia in different tracts of the affected posterior canal or by anatomical anomalies or structural changes of semicircular canals, such as stenosis and fibrosis, as high definition MRI and micro-CT three-dimensional reconstruction have suggested 17,18 .…”

“…7. Posterior canal light cupula [9][10][11] . "Light cupula" is characterised by a cupula with a specific gravity lower than the endolymph.…”

Nystagmus

“…New insights into mechanisms of the light cupula syndrome were described in two case reports: whereas heavy endolymph was proposed as a mechanism for persistent positional vertigo and geotropic positional nystagmus in a patient with meningitis and high cerebrospinal fluid (CSF) protein [14], a light cupula of a posterior canal was suggested in a case with persistent torsional DBN [15]. Novel therapeutic strategies in geotropic DCPN include treatment with transcutaneous vagus nerve stimulation [16], that led the authors to propose a top-down mechanism that normalized lateral canal hyperexcitability.…”