Abnormal Head Impulse Test in a Unilateral Cerebellar Lesion

Area of Science:

• Neuroscience
• Ophthalmology
• Vestibular System

Background:

• Head impulse tests (HIT) are typically normal in patients with cerebellar lesions.
• Cerebellar disorders can present with vestibular symptoms.

Purpose of the Study:

• To investigate the utility of HIT in diagnosing cerebellar lesions affecting the vestibulo-ocular reflex (VOR).
• To differentiate cerebellar VOR impairment from peripheral vestibular disorders.

Main Methods:

• Case report of a 46-year-old male with progressive dizziness and imbalance.
• Bedside horizontal head impulse tests (HIT) revealed catch-up saccades.
• Bithermal caloric tests and rotatory chair test were performed.
• Magnetic Resonance Imaging (MRI) identified an inferior cerebellar lesion near the flocculus.

Main Results:

• Horizontal HIT showed catch-up saccades, more pronounced during rightward stimulation.
• Caloric and rotatory chair tests yielded normal results.
• MRI confirmed a cerebellar lesion in the inferior cerebellum near the flocculus.

Conclusions:

• Damage to the flocculus or its connections can selectively impair the VOR during high-speed stimuli, particularly on the contralesional side.
• Cerebellar signs accompanying abnormal HIT findings aid in distinguishing cerebellar from peripheral vestibular lesions.