Gaze-evoked Horizontal (Sidebeat) Nystagmus

    • Horizontal jerk nystagmus that appears on side gaze
    • Fast phase of nystagmus is always in the direction of gaze
    • Common causes: systemic medications, brain stem or cerebellar stroke/tumor/inflammation, neurodegenerative and paraneoplastic disorders
    • Uncommon causes: Wernicke encephalopathy, hypomagnesemia, thiamine or cyanocobalamin deficiency, toxicity from phenytoin, lithium, or carbamazepine
    • Core clinical features
      • No symptoms from this form of nystagmus because it appears chiefly in side gaze
      • Horizontal jerk nystagmus present on side gaze to one or both sides
      • Nystagmus fast phase is always in the direction of gaze
      • Occlusion of the eyes and high-plus (Frenzel) lenses do not increase nystagmus amplitude (unlike in Peripheral Vestibular Nystagmus)
    • Possible accompanying clinical features
      • Upbeat nystagmus in upgaze
      • Downbeat nystagmus in downgaze
      • Ataxia
      • Skew deviation
      • Saccadic pursuit
      • Reduced consciousness
    • Rare variant called Periodic Alternating Nystagmus (PAN) displays a primary gaze position nystagmus fast phase that changes directions every 2 minutes
    • Rare variant called Rebound Nystagmus displays nystagmus with a fast phase in the direction of eccentric gaze, but when the eyes return to primary gaze position, the fast phase changes to the opposite direction
    • Brain MRI may show structural abnormalities
    • Peripheral vestibular nystagmus
    • Infantile motor nystagmus
    • Infantile sensory nystagmus
    • Ocular flutter or opsoclonus
    • Ocular dysmetria
    • Square wave jerks
    • Rule out toxicity from medication or vitamin deficiency states, especially Wernicke encephalopathy
    • Tip: Wernicke encephalopathy is on the top of the diagnostic list for virtually every form of nystagmus because it can be neurologically debilitating if left untreated and highly and rapidly reversible if promptly and properly treated!
    • Look for accompanying neurologic or systemic manifestations
    • Order brain MRI
    • If basic studies are unrevealing, order lumbar puncture, paraneoplastic panel
    • Treatment must be directed at the underlying cause
    • Medication directed at this form of nystagmus is unnecessary as the nystagmus causes no symptoms

    Nystagmus

    Overview Video Nystagmus Overview Physiologic Nystagmus Infantile Motor Nystagmus Infantile Sensory Nystagmus Monocular Pendular Nystagmus of Childhood Spasmus Nutans Peripheral Vestibular Nystagmus Gaze-evoked Horizontal (Sidebeat) Nystagmus Upbeat Nystagmus Downbeat Nystagmus Acquired Binocular Pendular Nystagmus