Makindo Medical Notes

A peripheral cause corrects and central cause remains focused

Head Impulse Test (HIT)

• The Head Impulse Test (HIT), also known as the Head Thrust Test, is a clinical test used to assess the function of the vestibulo-ocular reflex (VOR), which helps stabilize gaze during rapid head movements.
• It is especially useful in distinguishing between peripheral and central causes of vertigo.

Purpose

• The HIT is used to evaluate the ability of the vestibular system, particularly the semicircular canals, to detect head movement and coordinate eye movements.
• It is commonly used to help diagnose vestibular disorders such as vestibular neuritis (a peripheral cause of vertigo) and to rule out central causes like posterior circulation stroke.

Procedure

• The examiner instructs the patient to focus on a target (e.g., the examiner’s nose).
• The examiner then rapidly turns the patient's head 10–20 degrees to one side and observes the patient's eye movements.
• The patient’s head is quickly returned to the center, and the examiner repeats the procedure in the opposite direction.

Interpretation of Results

• Normal VOR (Central Cause Likely): : The patient’s eyes remain fixed on the target during the rapid head movement. This suggests intact vestibular function and raises suspicion for a central cause (e.g., stroke).
• Abnormal VOR (Peripheral Cause Likely): The patient’s eyes move with the head and then perform a quick corrective saccade back to the target. This is called a "corrective saccade" and suggests a peripheral vestibular lesion, such as vestibular neuritis.

Key Points

• In the context of constant vertigo, an abnormal Head Impulse Test supports a diagnosis of a peripheral cause (e.g., vestibular neuritis).
• A normal Head Impulse Test in a patient with vertigo may suggest a central cause (e.g., posterior circulation stroke), and further neuroimaging may be needed.