What is the expected finding on physical exam in a patient suspected of having a cerebellar stroke when their head is rapidly turned while focusing on a distant target?

Head Impulse Test Findings in Cerebellar Stroke

In a patient with cerebellar stroke, the head impulse test will show that the patient's eyes remain on the target (normal vestibulo-ocular reflex), which is the hallmark finding that distinguishes central causes like cerebellar stroke from peripheral vestibular disorders 1, 2.

Understanding the Head Impulse Test Mechanism

The head impulse test (h-HIT) evaluates the vestibulo-ocular reflex (VOR) by rapidly rotating the patient's head while they fixate on a distant target 1, 2. In cerebellar stroke:

• The VOR remains intact because the peripheral vestibular apparatus and its immediate brainstem connections are not damaged 1, 2
• Eyes stay fixed on the target during rapid head movements without requiring corrective saccades 1, 2
• A negative h-HIT (normal VOR) strongly suggests a central lesion with 91% of stroke patients demonstrating this finding 1

The HINTS Examination Protocol

The head impulse test is most powerful when combined with two other bedside findings in the HINTS examination (Head-Impulse-Nystagmus-Test-of-Skew) 2:

• Normal head impulse test (eyes remain on target) suggests central pathology 2
• Direction-changing nystagmus in eccentric gaze (horizontal nystagmus that beats right with rightward gaze, left with leftward gaze) indicates central lesion 3, 2
• Skew deviation (vertical ocular misalignment on alternate cover test) predicts brainstem involvement and occurs in 30% of brainstem strokes 2

The complete HINTS examination is 100% sensitive and 96% specific for stroke when any of these three findings are present, making it more sensitive than early MRI diffusion-weighted imaging which can be falsely negative in 12% of cases within 48 hours 2.

Critical Diagnostic Pitfall

While a positive h-HIT (abnormal VOR with corrective saccades) typically indicates peripheral vestibular pathology like vestibular neuritis, 9% of stroke patients can have a positive h-HIT 1. This occurs specifically with:

• Vestibulocerebellar strokes 1
• Pontocerebellar strokes 1
• Lateral pontine lesions affecting vestibular nuclei 1, 2

This is why the complete HINTS examination is essential - skew deviation correctly identified brainstem stroke in 2 of 3 cases where an abnormal h-HIT falsely suggested peripheral localization 2.

Additional Central Findings to Assess

Beyond HINTS, other examination findings that support cerebellar stroke include 3:

• Downbeating nystagmus on Dix-Hallpike maneuver without torsional component 3
• Baseline spontaneous nystagmus without provocative maneuvers 3
• Severe truncal instability out of proportion to peripheral causes 1
• Associated neurologic deficits including dysarthria, dysmetria, dysphagia, or sensory/motor loss 3

Clinical Context for High-Risk Patients

In this patient with hypertension, previous strokes, and diabetes presenting with acute vertigo, the pretest probability of stroke is substantially elevated 2. The presence of multiple vascular risk factors mandates:

• Immediate HINTS examination at bedside before imaging 2
• Urgent MRI with diffusion-weighted imaging as the gold standard, though CT may be performed first to exclude hemorrhage 4
• Do not rely on initial negative MRI if obtained within 48 hours, as 12% of cerebellar strokes show false-negative DWI early 2