Clinicopathologic Correlation in Lateral Medullary Stroke with Transient Ocular Motor Findings Mimicking Peripheral Vestibular Dysfunction (P6.315)

Objective: To report a patient with a rostral, lateral medulla stroke (LMS) with transient peripheral vestibulopathy (PV). The medial vestibular nucleus neurons (MVN) close to the stroke core appeared pathologically normal, suggesting that the initial vestibular signs related to transient ischemia. Background: Unilaterally decreased horizontal vestibulo-ocular reflex (h-VOR) gain occurs with peripheral vestibular lesions or lateral pontine strokes involving the fascicle or MVN. Vestibular reflexes are typically normal in (LMS). We describe clinicopathologic findings in an unusual LMS presenting transient unidirectional nystagmus and decreased h-VOR gain, mimicking PV. Methods: 61 year-old man admitted to ICU with an acute vestibular syndrome accompanied by aphonia and respiratory distress. He had right-beating nystagmus obeying Alexander’s law, an abnormal leftward head impulse test (HIT) confirmed quantitatively by video-oculography, and no skew deviation. He had severe axial lateropulsion and Horner’s syndrome. MRI showed a left LMS extending rostrally to the ponto-medullary junction and dorsally to near the MVN. The nystagmus subsided within two days and the horizontal HIT normalized clinically. Three weeks after discharge to rehabilitation, he died of sudden cardio-respiratory arrest. After autopsy, brainstem sections were stained with Luxol Fast Blue, H&E and neurofilament. To explain the ocular motor and vestibular findings, we hypothesized that the MVN was involved pathologically. Results: Neuropathological examination showed a left LMS whose extent matched that seen by imaging. Non-ocular motor signs correlated well with structures affected by the infarction. The nearby MVN, however, was spared. The left vertebral artery was occluded and the right was hypoplastic and 50[percnt] stenotic. Conclusion: We hypothesize that the ischemic penumbra of the LMS may have involved the MVN in the rostral medulla, leading to transiently abnormal h-VOR and unidirectional nystagmus. This is the first case of quantitatively proven abnormal horizontal-HIT during transient brainstem ischemia without pathologic infarction Disclosure: Dr. Kattah has received personal compensation for activities with Pfizer as a consultant. Dr. Saber Tehrani has nothing to disclose. Dr. Gujrati has nothing to disclose. Dr. Roeber has nothing to disclose. Dr. Newman-Toker has received personal compensation for activities with Sun Pharma Pharmaceuticals, India as a speaker. Dr. Newman-Toker has received research support from GN Otometrics and Interacoustics. Dr. Horn-Bochtler has nothing to disclose.