Downbeat Nystagmus Induced by Neck Extension in Chiari I Malformation.
Leonardo Ariello, David Patric Werner Rastall
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Case in brief
A 44-year-old woman had recurrent episodic vertigo reliably triggered by extending her neck. Standard positional maneuvers did not elicit symptoms or nystagmus, but adding cervical extension during testing produced reproducible positional downbeat nystagmus; she could also provoke both while seated by actively extending her neck. Brain MRI showed cerebellar tonsillar herniation consistent with Chiari I malformation. The stereotyped dependence on neck extension suggested a dynamic compression-related mechanism at the craniocervical junction rather than a gravity-dependent central vestibular disorder.
What made this case unusual
The downbeat nystagmus was elicited by cervical extension, including active extension while seated, but not by conventional positional maneuvers alone.
Diagnostic / clinical pearl
When positional downbeat nystagmus depends specifically on neck extension, consider the provoking mechanism and craniocervical junction pathology, not only a gravity-dependent central vestibular disorder.