Head Impulse Test
💡 Rule of thumb: In vertigo evaluation → Peripheral cause = corrective saccade, Central cause = eyes remain locked on target.
🎯 Head Impulse Test (HIT)
- The Head Impulse Test (HIT), also called the Head Thrust Test, assesses the vestibulo-ocular reflex (VOR), which stabilises gaze during rapid head movements. 👁️
- It is key in distinguishing between peripheral and central causes of vertigo. 🌀
🩺 Purpose
- Evaluates vestibular system function, especially the semicircular canals. 🔄
- Helps diagnose vestibular neuritis (peripheral vertigo) and rule out posterior circulation stroke (central vertigo). 🧠
⚙️ Procedure
- Ask patient to fix gaze on a stable target (usually examiner’s nose). 👃
- Examiner quickly turns the head 10–20° to one side, then back to centre. ➡️⬅️
- Repeat on the opposite side while observing eye movements. 👁️
📊 Interpretation
- Normal VOR ➝ Eyes stay on target:
🌐 Suggests central cause (e.g., posterior circulation stroke).
⚠️ This is sometimes called a “dangerous normal.”
- Abnormal VOR ➝ Eyes dragged with head, then corrective saccade:
🔄 Indicates peripheral lesion (e.g., vestibular neuritis, labyrinthitis).
This “catch-up saccade” is the hallmark of HIT positivity.
📌 Key Clinical Points
- In constant vertigo ➝ Abnormal HIT = peripheral cause, Normal HIT = central cause.
- Part of the HINTS exam (Head Impulse, Nystagmus, Test of Skew) 🧾, which is more sensitive than early MRI for posterior circulation stroke.
- Perform only if patient can safely tolerate rapid head movements (avoid in neck instability or cervical spine disease). 🚫
- Corrective saccades may be subtle ➝ repeat test, use fixation on nose, and compare both sides.
💡 Clinical Pearls
- 🚩 Red flag: Normal HIT in a patient with acute prolonged vertigo strongly suggests a central cause → urgent neuroimaging needed.
- 👂 HIT is most reliable in acute vestibular syndrome (constant vertigo, nausea, gait disturbance), less so in brief, positional vertigo (like BPPV).
- 🎥 Video Head Impulse Test (vHIT) can quantify deficits in semicircular canal function and is increasingly used in specialist clinics.
