How does the presence of nystagmus in a patient with dizziness help differentiate peripheral vestibular disorders from central neurologic causes, and what immediate management steps are recommended?

Nystagmus Characteristics Distinguish Peripheral from Central Vertigo

Nystagmus characteristics are the single most powerful bedside tool for differentiating peripheral vestibular disorders from central neurologic causes in dizzy patients, with specific patterns demanding immediate neuroimaging to prevent missing stroke.

Key Nystagmus Patterns That Differentiate Central from Peripheral Causes

Peripheral Vestibular Nystagmus (Benign Patterns)

• Peripheral nystagmus is horizontal with a rotatory (torsional) component, unidirectional (beats in the same direction regardless of gaze), suppressed by visual fixation, fatigable with repeated testing, and has a 5-20 second latency period before onset 1
• The nystagmus in peripheral disorders typically changes or resolves with repositioning maneuvers, distinguishing it from central causes 1
• Peripheral nystagmus is characteristic of BPPV (42% of all vertigo cases), vestibular neuritis (41% of peripheral vertigo), and Ménière's disease 1, 2

Central Vestibular Nystagmus (Red Flag Patterns)

• Pure vertical nystagmus (upbeating or downbeating) without any torsional component is a red flag for central pathology and mandates urgent diffusion-weighted MRI 1, 2
• Direction-changing nystagmus that switches direction without changes in head position (periodic alternating nystagmus) indicates central disease 1
• Baseline nystagmus present without any provocative maneuvers is a red flag for central causes 1, 2
• Central nystagmus is not suppressed by visual fixation and does not fatigue with repeated testing, helping distinguish it from peripheral patterns 3, 1
• Gaze-evoked nystagmus (nystagmus that changes direction with eccentric gaze) is typical of central lesions, particularly vertebrobasilar insufficiency 3, 1
• Downbeating nystagmus on Dix-Hallpike maneuver without a torsional component is a red flag demanding immediate neuroimaging 1, 2

Critical Associated Symptoms That Indicate Central Pathology

• Central vertigo is frequently accompanied by additional neurological symptoms including dysarthria, dysmetria, dysphagia, sensory or motor deficits, diplopia, or Horner's syndrome 1
• Severe postural instability with falling is a primary distinguishing feature of central vertigo, particularly vertebrobasilar insufficiency and cerebellar lesions 1
• New-onset severe headache with vertigo may indicate vertebrobasilar stroke or hemorrhage and requires immediate imaging 1, 2
• Sudden unilateral hearing loss accompanying vertigo is a red flag requiring urgent neuroimaging 2

The Dix-Hallpike Maneuver: Interpreting Results

Peripheral (BPPV) Pattern

• Characteristic peripheral findings include torsional and upbeating nystagmus with 5-20 second latency, crescendo-decrescendo pattern, fatigability with repeat testing, and resolution within 60 seconds 1, 4, 2
• When the Dix-Hallpike produces typical peripheral nystagmus, no imaging is indicated 1, 2

Central Pattern

• Immediate onset nystagmus (no latency), persistent nystagmus that does not fatigue, and purely vertical nystagmus without torsional component suggest central pathology requiring urgent MRI 1, 2
• Apogeotropic horizontal nystagmus on supine roll test or isolated positional downbeat nystagmus are red flags demanding immediate neuroimaging 1

Immediate Management Algorithm Based on Nystagmus Findings

When Nystagmus Indicates Peripheral Cause

• Perform canalith repositioning procedure (Epley maneuver) immediately for confirmed BPPV, with 80% success after 1-3 treatments and 90-98% success with repeat maneuvers 1, 2
• Do not prescribe vestibular suppressants for BPPV, as they prevent central compensation 1
• Reassess within 1 month to document resolution or persistence 1

When Nystagmus Indicates Central Cause

• Obtain MRI brain with diffusion-weighted imaging immediately—do not use CT, which has <1% diagnostic yield and misses most posterior circulation infarcts 1, 2
• Approximately 25% of patients with acute vestibular syndrome have cerebrovascular disease, rising to 75% in high vascular risk cohorts 1, 2
• Immediate neurologic consultation is mandatory 2

The HINTS Examination: Beyond Nystagmus Alone

• The HINTS examination (Head Impulse, Nystagmus, Test of Skew) has 100% sensitivity for detecting stroke when performed by trained practitioners, compared to only 46% sensitivity for early MRI 2, 5, 6
• The clinical HINTS examination is 94.0% sensitive and 86.9% specific for identifying central causes 6
• Components suggesting central vertigo include normal head impulse test (indicating intact vestibular function despite vertigo), direction-changing or vertical nystagmus, and present skew deviation 5, 6
• HINTS Plus adds bedside hearing assessment—sudden unilateral hearing loss with acute vestibular syndrome suggests stroke affecting the anterior inferior cerebellar artery territory 5, 6

Common Pitfalls to Avoid

• Approximately 10% of cerebellar strokes present similar to peripheral vestibular disorders, and 75-80% of patients with acute vestibular syndrome from posterior circulation infarct have no focal neurologic deficits on standard examination 1, 2
• Assuming a normal neurologic exam excludes stroke is incorrect—nystagmus characteristics are more sensitive than focal deficits 2
• Failure to respond to appropriate peripheral vertigo treatments (canalith repositioning) is a red flag indicating the underlying diagnosis may not be BPPV and warrants neuroimaging 3, 1
• Relying on patient descriptions of "spinning" versus "lightheadedness" is unreliable—focus on objective nystagmus patterns, timing, and triggers 2
• Direction-changing positional nystagmus can occasionally occur in peripheral disorders (9-20% of vestibular neuritis and Ménière's disease cases), but when combined with other central features, it strongly suggests central pathology 7

Special Clinical Scenarios Requiring Heightened Vigilance

Vertebrobasilar Insufficiency

• Isolated transient vertigo may precede vertebrobasilar stroke by weeks or months 3, 1
• Episodes typically last less than 30 minutes without associated hearing loss 3, 1
• Nystagmus does not fatigue and is not suppressed by gaze fixation, distinguishing it from peripheral causes 3, 1

Multiple Concurrent Vestibular Disorders

• Clinicians must consider the possibility of more than one vestibular disorder being present (e.g., BPPV with Ménière's disease or vestibular neuritis) 3, 1
• Atypical presentations or equivocal Dix-Hallpike findings warrant additional testing 1

High Vascular Risk Patients

• High vascular risk patients (age >50, hypertension, diabetes, prior stroke, atrial fibrillation) with acute vestibular syndrome require MRI even with normal neurologic examination, as 11-25% may have posterior circulation stroke 2, 6