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Abstract
The head impulse test (HIT) is used to evaluate the vestibulo-ocular reflex (VOR) during a high-velocity head rotation. Corrective catch-up saccades that occur during or after the HITs usually indicate peripheral vestibular hypofunction, whereas in acute vestibular syndrome, normal clinical (bedside) HITs should prompt a search for a central lesion. However, recent quantitative studies that evaluated HITs using magnetic search coils or video-based techniques have demonstrated that specific patterns of HIT abnormalities are associated with central vestibular disorders. While normal clinical HITs are typical of central lesions, discrepancies have been observed between clinical and quantitative HITs. The horizontal head impulse VOR gains can be significantly reduced unilaterally or bilaterally (positive HITs) in lesions involving the vestibular nucleus, nucleus prepositus hypoglossi, or flocculus. In diffuse cerebellar lesions, the VOR gain during horizontal head impulses may increase (hyperactive) with corrective saccades directed the opposite way. The presence of cross-coupled vertical corrective saccades during horizontal HITs is also suggestive of diffuse cerebellar lesions. Lesions involving the vestibular nucleus, medial longitudinal fasciculus, and cerebellum may show decreased or increased gains of the VOR during vertical HITs. Defining the differences in patterns observed during abnormal HITs may help practitioners localize the responsible lesions in both central and peripheral vestibulopathy.
Glossary
- AICA=
- anterior inferior cerebellar artery;
- CPA=
- cerebellopontine angle;
- h-HIT=
- horizontal head impulse test;
- HINTS=
- head impulse, nystagmus, and test of skew;
- HIT=
- head impulse test;
- MLF=
- medial longitudinal fasciculus;
- NPH=
- nucleus prepositus hypoglossi;
- PICA=
- posterior inferior cerebellar artery;
- PVP=
- position-velocity-pause;
- SCA=
- superior cerebellar artery;
- VOR=
- vestibulo-ocular reflex
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
- Received June 6, 2017.
- Accepted in final form January 2, 2018.
- © 2018 American Academy of Neurology
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