What causes horizontal and vertical nystagmus?

Causes of Horizontal and Vertical Nystagmus

Nystagmus is primarily caused by disorders affecting the vestibular system, including benign paroxysmal positional vertigo (BPPV), central nervous system lesions, and various otologic and neurologic conditions. 1, 2

Peripheral Vestibular Causes

Benign Paroxysmal Positional Vertigo (BPPV)

• Horizontal (Lateral Canal) BPPV:
  • Most common cause of horizontal nystagmus 2
  • Accounts for 5-15% of all BPPV cases 1
  • Two types:
    1. Geotropic type: Nystagmus beats toward the undermost (affected) ear
    2. Apogeotropic type: Nystagmus beats toward the uppermost ear 1
  • Diagnosed using the supine roll test, which reveals direction-changing nystagmus 1
  • Temporal profile: Paroxysmal with rapid onset (0-5 seconds), peak at 5-20 seconds, and complete resolution by 60 seconds 3

Other Peripheral Vestibular Disorders

• Ménière's disease: Causes episodic attacks with fluctuating hearing loss, aural fullness, tinnitus, and persistent apogeotropic horizontal nystagmus 1, 2, 3
• Vestibular neuritis/Labyrinthitis: Produces unidirectional horizontal nystagmus 1, 4
• Perilymphatic fistula: Causes vertigo and nystagmus triggered by pressure changes 2
• Superior canal dehiscence syndrome: Results in pressure-induced rather than position-induced vertigo 1, 2
• Posttraumatic vertigo: Can produce various nystagmus patterns depending on the structures affected 1

Central Nervous System Causes

Brainstem and Cerebellar Disorders

• Downbeat nystagmus: Vertical nystagmus with fast phase downward

  • Most often caused by bilateral floccular lesions or dysfunction 5, 6
  • Common in cerebellar disorders 6

• Upbeat nystagmus: Vertical nystagmus with fast phase upward

  • Caused by lesions in the midbrain or medulla 5, 6

• Posterior circulation stroke/TIA: Can present with:

  • Direction-changing nystagmus without changes in head position 2
  • Isolated vertigo in up to 25% of cases (75% in high vascular risk patients) 2

• Cerebellar lesions: Small lesions in the lower cerebellum can cause:

  • Unidirectional horizontal nystagmus toward the side of the lesion
  • Direction-changing apogeotropic positional nystagmus 4

Other Neurologic Disorders

• Multiple sclerosis: Produces various forms of nystagmus, including horizontal nystagmus 1, 2
• Demyelinating diseases: Affect central vestibular pathways 1
• Vertebrobasilar insufficiency: Causes transient episodes of nystagmus 2
• Vestibular migraine: Results in persistent geotropic or apogeotropic horizontal nystagmus 3

Other Causes

Medication and Toxic Causes

• Medication side effects: Various medications can induce nystagmus 1, 2
• Alcohol intoxication: Common cause of horizontal gaze-evoked nystagmus 2
• Toxic exposures: Can affect vestibular function 2

Metabolic and Other Conditions

• Metabolic disorders: Particularly electrolyte abnormalities like hyponatremia 2
• Anxiety or panic disorder: Can exacerbate vestibular symptoms 1
• Cervicogenic vertigo: Can be associated with nystagmus 1
• Postural hypotension: May contribute to dizziness with positional changes 1

Diagnostic Approach

When evaluating nystagmus, clinicians should consider:

1. Nystagmus characteristics:

   • Direction (horizontal, vertical, torsional, or mixed)
   • Timing (paroxysmal vs. persistent)
   • Triggers (positional changes, pressure changes, etc.)

2. Red flags for central causes:

   • Direction-changing nystagmus without head position changes
   • Gaze-holding nystagmus
   • Direction-switching nystagmus
   • Baseline nystagmus without provocative maneuvers 2
   • Failure to respond to canalith repositioning procedures 2

3. Key diagnostic tests:

   • Supine roll test: For lateral canal BPPV 1
   • Dix-Hallpike maneuver: For posterior canal BPPV
   • HINTS exam: For Acute Vestibular Syndrome (higher sensitivity than early MRI for stroke) 2

Understanding the specific pattern, direction, and triggers of nystagmus is crucial for accurate diagnosis and appropriate treatment of the underlying cause.