How do I differentiate between a posterior circulation stroke and a peripheral cause in a patient presenting with sudden onset vertigo, weakness, or difficulty with speech?

Differentiating Posterior Circulation Stroke from Peripheral Vertigo

Assume posterior circulation stroke until proven otherwise in any patient with acute vestibular syndrome (continuous vertigo/dizziness lasting days), especially those over 50 or with vascular risk factors, because 11-25% of these patients have stroke even with a normal neurologic examination, and missing this diagnosis carries mortality rates of 45-86%. 1, 2

Critical First Step: Classify the Vestibular Syndrome

The timing pattern is more diagnostically valuable than the patient's subjective description of "dizziness" 1, 3:

• Brief episodic vertigo (seconds to minutes, triggered by head movements): Almost always BPPV—no imaging needed if Dix-Hallpike is positive 1, 3
• Acute vestibular syndrome (AVS) (continuous symptoms lasting days to weeks): This is the HIGH-RISK category where stroke must be excluded 1, 4
• Spontaneous episodic vertigo (minutes to hours, recurrent): Consider Ménière's disease or vestibular migraine 2, 3

Red Flags Mandating Immediate Stroke Workup

Any of these features require urgent MRI brain without contrast 1, 2, 3:

• Focal neurologic deficits: Diplopia, dysphagia, dysarthria, facial weakness, limb weakness 1, 2
• Truncal ataxia (inability to sit/stand unsupported): Most common sign in NIHSS 0 posterior circulation strokes 1
• New severe headache with vertigo 1, 3
• Sudden unilateral hearing loss 2, 3
• Pure vertical or direction-changing nystagmus (strongly suggests central cause) 2
• Age >50 with vascular risk factors (hypertension, diabetes, atrial fibrillation, prior stroke) presenting with AVS 1, 2

The HINTS Examination: Your Most Powerful Bedside Tool

Only use HINTS in patients with continuous vertigo AND ongoing nystagmus (acute vestibular syndrome) 1, 5:

HINTS Components:

1. Head Impulse Test: Normal (corrective saccade absent) = CENTRAL cause 2, 3
2. Nystagmus: Direction-changing or pure vertical = CENTRAL cause 2
3. Test of Skew: Vertical skew deviation present = CENTRAL cause 2, 3

When performed by trained practitioners, HINTS has 100% sensitivity for stroke (better than early MRI at 46%) 1, 3. However, when performed by non-experts, reliability drops significantly 1, 3.

HINTS Interpretation Algorithm:

• ANY central feature (normal head impulse, direction-changing nystagmus, OR skew deviation) → Obtain MRI immediately 2, 3
• ALL peripheral features in low-risk patient by trained examiner → No imaging needed 1, 3
• Uncertain or performed by non-expert → Default to imaging in patients with vascular risk factors 1, 3

Key Distinguishing Clinical Features

Peripheral Causes (Vestibular Neuritis, Labyrinthitis, BPPV):

• Auditory symptoms (tinnitus, hearing loss, aural fullness) strongly favor peripheral 2
• Horizontal or horizontal-rotatory nystagmus 2
• Abnormal head impulse test (corrective saccade present) 2, 3
• Symptoms triggered by position changes (BPPV) 1, 3
• No focal neurologic deficits 2

Posterior Circulation Stroke:

• Can present with NIHSS score of 0 (headache, vertigo, nausea only) 1
• 75-80% have NO focal neurologic deficits on initial presentation 1, 3
• Isolated truncal ataxia is the most common sign in subtle presentations 1
• Loss of consciousness, somnolence 1
• Crossed neurologic signs (ipsilateral cranial nerve + contralateral motor/sensory) 6
• Visual field defects, skew deviation, convergence nystagmus 1

Common Pitfalls to Avoid

1. Never assume normal neurologic exam excludes stroke: Up to 80% of posterior circulation strokes lack focal deficits initially 1, 3
2. Don't rely on NIHSS: It underestimates posterior circulation strokes because it emphasizes limb/speech over cranial nerves 1
3. Never use CT as definitive rule-out: CT has <1% diagnostic yield for isolated dizziness and misses most posterior circulation infarcts 1, 3
4. Don't perform HINTS on patients without continuous symptoms: It's only validated for acute vestibular syndrome 1, 5
5. Isolated vertigo IS a stroke presentation: 25% of posterior circulation strokes present as isolated vestibular syndrome 4

Imaging Strategy

When to Image:

• MRI brain without contrast (preferred): For AVS with abnormal HINTS, vascular risk factors, or any red flags 1, 2, 3
• MRI has 4% diagnostic yield vs <1% for CT in isolated dizziness 1, 3
• Diffusion-weighted imaging is essential but may be negative in first 24-48 hours 1, 4

When NOT to Image:

• Typical BPPV with positive Dix-Hallpike and no red flags 1, 3
• AVS with all peripheral HINTS features by trained examiner in low-risk patient 1, 3

Practical Clinical Algorithm

For any patient with acute continuous vertigo:

1. Check vital signs and vascular risk factors (age >50, hypertension, diabetes, atrial fibrillation) 1, 2
2. Perform focused neurologic exam: Test truncal ataxia (sitting/standing balance), cranial nerves, limb coordination 1
3. If ANY red flag present → MRI brain immediately 1, 2
4. If no red flags but high vascular risk → MRI brain within 24 hours 1, 2
5. If low risk and trained in HINTS → Perform HINTS; if all peripheral features, observe and reassess 1, 3
6. If uncertain or non-expert → Default to MRI for patients >50 or with any vascular risk factors 1, 2

The stakes are too high to miss: Posterior circulation strokes have 45-86% mortality without treatment, but good outcomes occur in only 20% even with advanced care 1. When in doubt, image.