Positional and positioning down-beating nystagmus without central nervous system findings

Area of Science:

• Neurology
• Ophthalmology
• Vestibular System

Background:

• Positional down-beating nystagmus (p-DBN) is typically associated with central nervous system disorders.
• Anterior semicircular canal (ASC) canalithiasis has been proposed as a cause of p-DBN, leading to a diagnosis of ASC benign paroxysmal positional vertigo (BPPV).

Observation:

• Four cases of p-DBN were observed in head-hanging or supine positions.
• Patients showed no neurological abnormalities or brain MRI changes.
• Nystagmus was position-specific, lacking gaze nystagmus, and did not reverse upon sitting up.

Findings:

• The observed nystagmus presented with latency, minimal torsion, and decreased over time.
• These clinical features raise questions about the definitive diagnosis of ASC-BPPV in cases without evident central nervous system dysfunction.
• The etiology of p-DBN in these specific cases remains difficult to ascertain.

Implications:

• This study highlights diagnostic challenges in cases of p-DBN without clear central nervous system involvement.
• It suggests a need for further research into the underlying mechanisms of p-DBN.
• Re-evaluation of diagnostic criteria for anterior semicircular canal benign paroxysmal positional vertigo may be warranted.