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Down-beat nystagmus and its causes

Down-beat nystagmus is a central vestibular disorders -Pitch plane disorder.

It is a Jerk nystagmus with fast phase downwards.

Most prominent on looking down & out.

What is the site of lesion in downbeat nystagmus?

Site of lesion in down gaze nystagmus is disruption of posterior SCC projections secondary to Lesions

in the floor of fourth ventricle.

  • Bilateral lesions of the flocculi

What are the causes of Downbeat nystagmus?

  1. Lesions of cervico-medullary junction - ACM.
  2. Lesions of flocculus, paraflocculus, nodule, uvula & medulla.
  3. Spinocerebellar ataxia.
  4. Metabolic causes.
    Wernicke's encephalopathy.
    Deficiency of magnesium, thiamine, Vit B12.
  1. Toxic.
    Lithium, Phenytoin, CBZ, morphine, amiodarone.
    Alcohol intoxication.