Chiari I畸形中颈部后仰诱发的下跳性眼震

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中文摘要

目的： 描述一种与Chiari I畸形（CMI）相关的、由颈部后仰诱发的体位性下跳性眼震（DBN）。
患者： 一名44岁女性，反复发作性眩晕，可由颈部后仰可重复诱发。
干预措施： 床旁眼动检查、体位试验、视频眼震图以及脑磁共振成像（MRI）。
主要结局指标： 体位性眼震的特征描述及其诱发机制的确定。
结果： 仅常规体位手法未能诱发症状或眼震。只有在体位手法期间叠加额外的颈部后仰时，才观察到可重复的体位性DBN。患者坐位时主动后仰颈部也能可靠地诱发症状和DBN。脑MRI显示小脑扁桃体下疝，符合CMI。
结论： 由颈部后仰诱发的体位性DBN应不仅考虑中枢性体位性眼震，还应考虑导致该中枢表型的潜在机制。在该患者中，对颈部后仰的高度刻板依赖性提示颅颈交界处存在动态压迫相关机制，而非重力依赖的中枢前庭疾病。

英文摘要

OBJECTIVE: To describe a cervical extension-triggered form of positional downbeat nystagmus (DBN) associated with Chiari I malformation (CMI).
PATIENT: A 44-year-old woman with recurrent episodic vertigo reproducibly triggered by neck extension.
INTERVENTIONS: Bedside ocular motor examination, positional testing, video-oculography, and brain magnetic resonance imaging (MRI).
MAIN OUTCOME MEASURES: Characterization of positional nystagmus and identification of its provoking mechanism.
RESULTS: Conventional positional maneuvers alone failed to provoke symptoms or nystagmus. Reproducible positional DBN was observed only when additional cervical extension was superimposed during positional maneuvers. The patient could also reliably trigger symptoms and DBN through active neck extension while seated. Brain MRI demonstrated cerebellar tonsillar herniation consistent with CMI.
CONCLUSIONS: Positional DBN triggered by cervical extension should prompt consideration not only of central positional nystagmus, but also of the underlying mechanism responsible for the central phenotype. In this patient, the highly stereotyped dependence on neck extension suggested a dynamic compression-related mechanism at the craniocervical junction rather than a gravity-dependent central vestibular disorder.