What are the most common causes of horizontal nystagmus?

Most Common Causes of Horizontal Nystagmus

The most common causes of horizontal nystagmus include benign paroxysmal positional vertigo (BPPV) of the horizontal canal, vestibular neuritis/labyrinthitis, central nervous system disorders, medication side effects, and alcohol intoxication. 1

Peripheral Vestibular Causes

Benign Paroxysmal Positional Vertigo (BPPV)

• Horizontal (lateral) canal BPPV accounts for 10-15% of all BPPV cases 2, 1

• Two main types:

  1. Geotropic type (more common):
     • Nystagmus beats toward the undermost (affected) ear
     • More intense when lying on the affected side
     • Changes direction when rolling to the opposite side but remains geotropic
  2. Apogeotropic type (less common):
     • Nystagmus beats toward the uppermost ear
     • Changes direction when rolling to the opposite side but remains apogeotropic

• Diagnosed using the supine roll test:

  1. Patient lies supine with head in neutral position
  2. Head is quickly rotated 90 degrees to one side
  3. Observe for nystagmus
  4. Return head to neutral position
  5. Rotate head 90 degrees to opposite side
  6. Observe for nystagmus 2

Other Peripheral Vestibular Disorders

• Vestibular neuritis/Labyrinthitis: Produces unidirectional horizontal nystagmus 1
• Ménière's disease: Causes episodic attacks with persistent apogeotropic horizontal nystagmus 1, 3
• Posttraumatic vertigo: Can produce various nystagmus patterns depending on structures affected 1

Central Causes

• Brainstem and cerebellar stroke: Presents with direction-changing nystagmus without changes in head position 1
• Multiple sclerosis: Produces various forms of nystagmus, including horizontal nystagmus 1
• Demyelinating diseases: Affect central vestibular pathways 1
• Posterior circulation stroke: Can present with isolated vertigo in up to 25% of cases 1

Non-Vestibular Causes

• Medication side effects: Various medications can induce nystagmus 1
• Alcohol intoxication: Common cause of horizontal gaze-evoked nystagmus 1
• Toxic exposures: Can affect vestibular function 1
• Metabolic disorders: Particularly electrolyte abnormalities like hyponatremia 1

Distinguishing Features Between Central and Peripheral Causes

Peripheral Nystagmus (BPPV)

• Latency period before onset (typically 0-5 seconds) 4, 3
• Paroxysmal in nature (brief duration with declining intensity)
• In horizontal canal canalolithiasis, nystagmus typically declines to near zero by 40-60 seconds 3
• Fatigability with repeated testing 4

Central Nystagmus

• No latency or very brief latency
• Persistent rather than paroxysmal
• At 40 seconds, SPV (slow-phase velocity) remains at 61% of peak in vestibular migraine 3
• Direction-changing without position changes
• Gaze-holding nystagmus
• Baseline nystagmus without provocative maneuvers 1

Clinical Pearls and Pitfalls

• Important diagnostic test: The HINTS exam (Head Impulse test, Nystagmus, Test of Skew) has higher sensitivity and specificity than early MRI for detecting stroke in patients with acute vestibular syndrome 1
• Common pitfall: Failing to recognize that horizontal canal BPPV can occur following repositioning maneuvers for posterior canal BPPV (canal switch) 2
• Diagnostic challenge: In some cases, it may be difficult to determine the affected side in horizontal canal BPPV by comparing nystagmus intensity alone; additional tests like the lying-down nystagmus test can help 5
• Warning sign: Failure to respond to canalith repositioning procedures should raise concern that the underlying diagnosis may not be BPPV 1