Is gaze evoked nystagmus a central or peripheral form of nystagmus?

Gaze-Evoked Nystagmus is a Central Form of Nystagmus

Gaze-evoked nystagmus (GEN) is definitively a central form of nystagmus, typically indicating pathology in the brainstem or cerebellum. 1

Characteristics and Localization of Gaze-Evoked Nystagmus

• GEN is characterized by nystagmus that occurs when the eyes are held in eccentric positions (away from primary gaze) 2
• It consists of a pathological slow drift back toward the primary position, followed by a corrective saccade in the direction of gaze 3
• GEN is a key indicator of central nervous system pathology, particularly affecting the neural integrator function responsible for gaze-holding 4

Anatomical Localization:

• Purely horizontal GEN indicates a pontomedullary lesion 4, 5
• Purely vertical GEN suggests a midbrain lesion 4, 5
• Generalized GEN (in all directions) typically indicates cerebellar dysfunction 5
• Specific cerebellar structures involved include the vermal pyramid, uvula, tonsil, parts of the biventer lobule, and the inferior semilunar lobule 6

Distinguishing Central from Peripheral Nystagmus

• Central nystagmus (including GEN) typically does not fatigue and is not easily suppressed by visual fixation, unlike peripheral nystagmus 1
• GEN is specifically mentioned as a typical finding in central lesions, particularly in vertebrobasilar insufficiency 1
• The American Academy of Otolaryngology-Head and Neck Surgery identifies GEN as a central finding that helps distinguish central from peripheral causes of vertigo 1

Clinical Implications and Associated Conditions

• GEN is commonly associated with:

  • Cerebellar disorders and ataxias 4, 5
  • Brainstem lesions 4
  • Medication effects, particularly antiepileptic drugs 5
  • Chronic alcohol abuse 5
  • Neurodegenerative diseases affecting the cerebellum 5
  • Vertebrobasilar insufficiency 1

• Direction-changing bilateral GEN (BGEN) is considered a more specific sign for central gaze-holding deficit than unilateral GEN (UGEN) 6

Diagnostic Approach

• When GEN is identified, neuroimaging (preferably MRI) is indicated to evaluate for structural lesions of the brainstem or cerebellum 1, 7
• CT scans may not adequately visualize posterior fossa structures, making MRI the preferred imaging modality 7
• A thorough neuro-ophthalmological examination should be performed to identify other associated central ocular motor abnormalities 8

Common Pitfalls and Caveats

• GEN must be distinguished from peripheral vestibular nystagmus, which typically has a torsional component and is suppressed by visual fixation 1
• The presence of GEN should raise suspicion for serious central pathology, particularly when accompanied by other neurological signs 1
• Failure to recognize GEN as a central sign may lead to missed diagnosis of potentially serious conditions such as vertebrobasilar insufficiency or cerebellar stroke 1
• GEN may coexist with other forms of nystagmus, complicating the clinical picture 8

In summary, gaze-evoked nystagmus is a definitive central form of nystagmus that localizes to specific areas within the brainstem and cerebellum, serving as an important clinical sign for identifying central nervous system pathology.