Eye movement abnormalities in middle cerebellar peduncle strokes.

The middle cerebellar peduncle (MCP) is a major conduit for cortico-ponto-cerebellar fibers that convey information related to eye movements. This study aims to elucidate eye movement abnormalities that arise from lesions confined to the MCP. In 23 patients with acute strokes restricted to unilateral MCPs, we investigated the clinical features and ocular motor findings including spontaneous nystagmus, saccades, smooth pursuit, ocular tilt reaction, and head impulse tests. Bithermal caloric tests and audiometry were also performed. Patients with strokes restricted to the MCP usually developed acute vertigo or imbalance, along with few sensorimotor signs or auditory symptoms. Patients frequently showed abnormal eye movements that included spontaneous horizontal/torsional nystagmus, ocular tilt reaction, gaze-evoked nystagmus, abnormal head impulse responses, and bilaterally impaired horizontal smooth pursuit. Unilateral MCP strokes produce acute vertigo and imbalance with distinct ocular motor abnormalities, which are primarily caused by damage to the central vestibular structures and by disruption of the neural pathways responsible for eye-position stabilization and smooth pursuit.