What is the most likely diagnosis for a 57-year-old man presenting with sudden onset dizziness, vomiting, and bidirectional nystagmus, with a medical history of diabetes, hypertension, and vascular claudication?

Cerebellar Stroke

This patient most likely has a cerebellar stroke, not a peripheral vestibular disorder. The combination of bidirectional nystagmus, skew deviation on test of skew, absent corrective saccade on head impulse test (negative HIT), and significant vascular risk factors (diabetes, hypertension, vascular claudication) in a 57-year-old man with acute persistent vertigo strongly indicates a central (posterior circulation) cause rather than a peripheral vestibular etiology 1, 2, 3.

Key Diagnostic Features Pointing to Central Cause

The HINTS examination findings are pathognomonic for central vertigo:

• Bidirectional nystagmus is a hallmark of central pathology and essentially rules out peripheral causes like vestibular neuritis or labyrinthitis, which produce unidirectional horizontal nystagmus 4, 5
• Skew deviation on test of skew indicates brainstem or cerebellar involvement affecting vestibular supranuclear pathways 6
• Absent corrective saccade on head impulse test (negative HIT) paradoxically suggests a central lesion when combined with other central signs, as peripheral vestibular loss typically produces a positive HIT with corrective saccades 1, 2

This triad constitutes an abnormal HINTS examination with 100% sensitivity for posterior circulation stroke when performed by trained practitioners, compared to only 46% sensitivity for early MRI 1, 2.

Why Not Peripheral Causes

Benign paroxysmal positional vertigo (BPPV) is excluded because:

• BPPV causes brief episodic vertigo lasting seconds to minutes, not continuous symptoms for 2 hours 1
• BPPV produces positional torsional or direction-changing horizontal nystagmus only with provocative maneuvers, not bidirectional nystagmus at rest 4
• BPPV does not cause skew deviation 6

Labyrinthitis and vestibular neuritis are excluded because:

• These peripheral vestibulopathies produce unidirectional horizontal nystagmus with a torsional component, not bidirectional nystagmus 4, 7, 5
• Peripheral vestibular disorders cause a positive head impulse test with corrective saccades toward the affected side 1, 2
• Peripheral causes do not produce skew deviation 6

Critical Risk Factor Profile

This patient's vascular risk factors dramatically increase stroke probability:

• Diabetes, hypertension, and vascular claudication are established cardiovascular risk factors that significantly elevate posterior circulation stroke risk 6, 3
• The prevalence of cerebrovascular disease in patients presenting with acute vestibular syndrome may be as high as 75% in high vascular risk cohorts 2
• Stroke accounts for 3-7% of all vertigo cases overall, but this percentage is substantially higher in patients with multiple vascular risk factors 8, 5

Common Pitfall to Avoid

A critical error would be assuming this is peripheral vestibular disease based solely on the chief complaint of vertigo and vomiting. Up to 75-80% of patients with acute vestibular syndrome from posterior circulation infarct have no focal neurologic deficits beyond the vestibular findings 1, 2. Nausea and vomiting occur with both peripheral and central causes, particularly with strokes in the brainstem or cerebellum 6, 5.

Immediate Management

This patient requires emergent MRI brain without contrast to confirm cerebellar or brainstem infarction 1, 2. CT head has only 20-40% sensitivity for detecting posterior circulation infarcts and should not be relied upon to exclude stroke 1, 2. The patient should be managed according to acute ischemic stroke protocols, including consideration for thrombolysis if within the appropriate time window 6, 3.