What are the possible causes of horizontal nystagmus?

Horizontal Nystagmus: Causes and Clinical Approach

Horizontal nystagmus has both peripheral and central causes that must be systematically differentiated, with the most common peripheral causes being lateral canal BPPV (5-15% of BPPV cases) and vestibular neuritis, while central causes include posterior circulation stroke, vestibular migraine, and cerebellar/brainstem lesions.

Peripheral Causes of Horizontal Nystagmus

Lateral (Horizontal) Canal BPPV

• Direction-changing horizontal nystagmus provoked by supine roll testing 1
• Geotropic pattern (beating toward ground): stronger nystagmus indicates affected ear
• Apogeotropic pattern (beating away from ground): side opposite strongest nystagmus is affected
• Paroxysmal onset (typically <1 second), duration 12-48 seconds, fatigues by 60 seconds 2
• Peak slow-phase velocity occurs at 5-20 seconds 2

Vestibular Neuritis

• Unidirectional horizontal nystagmus without positional provocation 3
• Beats away from affected side
• Persistent, does not fatigue
• No hearing loss (distinguishes from labyrinthitis)
• Acute onset with continuous vertigo lasting days

Other Peripheral Causes

• Ménière's disease: episodic vertigo with fluctuating hearing loss, tinnitus, aural fullness 4
• Perilymph fistula: pressure-triggered episodes, may follow ear surgery 1
• Superior canal dehiscence: pressure/sound-induced symptoms 1

Central Causes of Horizontal Nystagmus

Red Flags for Central Pathology 1, 4

Critical distinguishing features:

• Direction-changing nystagmus WITHOUT head position changes (periodic alternating nystagmus)
• Gaze-evoked nystagmus (beats toward direction of gaze)
• Baseline nystagmus without provocative maneuvers
• Does not fatigue and not suppressed by visual fixation
• Associated neurological signs: dysarthria, dysmetria, dysphagia, sensory/motor deficits, Horner's syndrome

Specific Central Etiologies

Posterior Circulation Stroke/TIA 1, 4

• 10% of cerebellar strokes mimic peripheral vestibular processes 1
• Sudden onset, more abrupt than vestibular neuritis
• Gaze-evoked nystagmus typical
• Severe postural instability
• Additional posterior circulation signs usually present

Vestibular Migraine 1, 4

• Accounts for up to 14% of vertigo cases
• Diagnostic criteria: ≥5 episodes lasting 5 minutes-72 hours, migraine history, ≥50% of episodes with migraine features (headache, photophobia, phonophobia, aura)
• Can show persistent geotropic or apogeotropic horizontal nystagmus 2
• At 40 seconds, nystagmus maintains 61% of peak velocity (versus <2% in BPPV) 2

Cerebellar/Brainstem Lesions 5, 6, 3

• Central positional nystagmus accounts for up to 12% of positional nystagmus cases 5
• Often downward-beating or apogeotropic in lateral positions
• Persistent rather than paroxysmal
• Associated with gaze-evoked nystagmus in all directions (indicates cerebellar dysfunction) 6
• Causes: stroke, tumors, demyelination, degenerative diseases, autoimmune/paraneoplastic conditions

Vertebrobasilar Insufficiency 4

• Episodes typically <30 minutes
• No hearing loss
• Gaze-evoked nystagmus
• Does not fatigue or suppress with fixation
• May precede stroke by weeks to months

Diagnostic Algorithm

Step 1: Characterize the Nystagmus Pattern

• Provoked by Dix-Hallpike: If torsional upbeating → posterior canal BPPV
• Provoked by supine roll test: If direction-changing horizontal → lateral canal BPPV
• Spontaneous without provocation: Consider vestibular neuritis (peripheral) vs. central causes

Step 2: Assess Temporal Profile 2

• Paroxysmal (onset <1s, resolves by 60s): Strongly suggests canalolithiasis
• Persistent (maintains >60% intensity at 40s): Consider cupulolithiasis, vestibular migraine, or central causes

Step 3: Check for Central Features 1, 4

• Perform complete neurological examination
• Look for: dysarthria, limb ataxia, sensory deficits, cranial nerve palsies
• Test gaze-holding function
• Assess for direction-changing nystagmus without head movement

Step 4: Evaluate Response to Treatment

• Failure to respond to canalith repositioning procedures raises concern for non-BPPV diagnosis 1, 4
• Consider central pathology or alternative peripheral causes

Common Pitfalls to Avoid

1. Assuming all positional horizontal nystagmus is BPPV: Central positional nystagmus can mimic lateral canal BPPV 5

2. Missing posterior circulation stroke: 10% present like peripheral vestibular disease; maintain high suspicion with vascular risk factors 1

3. Overlooking vestibular migraine: Persistent horizontal nystagmus that doesn't fatigue appropriately should prompt consideration 2

4. Ignoring subtle neurological signs: Carefully examine for cerebellar signs (truncal ataxia, dysmetria) and brainstem signs 3

5. Not performing supine roll test: Missing this test results in undiagnosed lateral canal BPPV when Dix-Hallpike is negative 1

When Imaging Is Indicated 1, 4

Do NOT obtain imaging for:

• Classic BPPV with typical nystagmus pattern and no additional symptoms

DO obtain MRI head without contrast for:

• Atypical nystagmus patterns (downbeating, direction-changing without position change)
• Associated neurological deficits
• Failure to respond to appropriate repositioning maneuvers
• High vascular risk factors with acute persistent vertigo
• Baseline nystagmus without provocation