Makindo Medical Notes

💡 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.