Upbeat Transitioning to Downbeat Nystagmus in Wernicke's Encephalopathy

This is a 30-year-old man with a history of alcohol abuse who presented to the hospital with inability to walk after several weeks of heavy drinking and malnutrition. While in the hospital, he noted that when he would look straight ahead, everything he saw would appear to be bouncing up and down - a common description of oscillopsia. In the hospital, he was found to have an upbeat nystagmus (UBN), as seen in the first part of the video. Given his alcohol abuse history, Wernicke's encephalopathy was diagnosed. He was given IV thiamine among other IV nutrition and fluids. Two months after hospitalization he initially noted improvement in his oscillopsia. However, despite continued supplementation with oral thiamine, in the coming months his oscillopsia worsened. He then presented to clinic around a year after the onset of the above symptoms. He was found to have a downbeat nystagmus (DBN), as seen in the second part of the video. His DBN increased on lateral gaze, and there was UBN in upgaze. On convergence, his DBN reversed to UBN, as seen in the third part of the video. Saccades were hypometric horizontally and vertically. Smooth pursuit and vestibulo-ocular reflex suppression were minimally impaired, and head impulse test was normal horizontally and vertically bilaterally. Other notable abnormal findings on the general neurological exam included a length-dependent loss of sensation to multiple modalities, decreased reflexes throughout, mild dysdiadochokinesia, and an abnormal tandem gait. While the triad of confusion, ophthalmoplegia, and ataxia is the neurologists' traditional description of Wernicke's encephalopathy, the eye movement abnormalities have been well described. The finding of an UBN acutely transforming into a DBN chronically is classic for Wernicke's encephalopathy [Kattah et al. 2019], and is thus a useful sign for the clinician to bear in mind. The UBN seen acutely may also transition with convergence to DBN. While this may have been present in our patient, it was clear that chronically, his DBN reversed to UBN with convergence. Another common finding is impaired horizontal vestibulo-ocular reflex, which was not seen in our patient in the chronic phase. MRI findings in Wernicke's encephalopathy include several abnormalities within the brainstem, including the T2 FLAIR hyperintensities in the periventricular region around the third ventricle, the periaqueductal gray, the tectal plate, and the dorsal medulla [Zuccoli et al. 2007]. Many structures within these lesioned areas are implicated in the control of eye movements. The theorized mechanism of the UBN in the acute phase is a lesion of the structures in the perihypoglossal complex, which are the nucleus intercalatus and the nucleus of Roller, located in the dorsal medulla. These structures inhibit the flocculus, a structure normally implicated in the downward slow phase bias of the eyes. Thus, this disinhibition of the flocculus leads to a downward slow phase and upward fast phase, or UBN. Nearby structures theoretically lesioned include the paramedian tract neurons. These normally excite the flocculus, which would lead to an upward bias and thus a DBN. It is theorized that these lesions of the nucleus intercalatus and/or the nucleus or Roller dominate over the lesions of the paramedian tract neurons acutely. As the patient recovers, these former areas may heal while the damage done to the paramedian tract neurons may be permanent. This subsequently leads to impaired excitation of the flocculus, which causes an upward slow phase bias, and thus a chronic DBN.