Nucleus prepositus hypoglossi lesions produce a unique ocular motor syndrome

Objective: To describe the ocular motor abnormalities in 9 patients with a lesion involving the nucleus prepositus hypoglossi (NPH), a key constituent of a vestibular-cerebellar-brainstem neural network that ensures that the eyes are held steady in all positions of gaze. Methods: We recorded eye movements, including the vestibulo-ocular reflex during head impulses, in patients with vertigo and a lesion involving the NPH. Results: Our patients showed an ipsilesional-beating spontaneous nystagmus, horizontal gaze-evoked nystagmus more intense on looking toward the ipsilesional side, impaired pursuit more to the ipsilesional side, central patterns of head-shaking nystagmus, contralateral eye deviation, and decreased vestibulo-ocular reflex gain during contralesionally directed head impulses. Conclusions: We attribute these findings to an imbalance in the NPH-inferior olive-flocculus-vestibular nucleus loop, and the ocular motor abnormalities provide a new brainstem localization for patients with acute vertigo.