The relationship between upbeat and downbeat nystagmus in Wernicke's encephalopathy

This patient presented with acute upbeat nystagmus (UBN) in the setting of alcoholism and malnutrition due to thiamine deficiency causing Wernicke's encephalopathy. It is common that a transition from UBN to downbeat nystagmus (DBN) can be seen with convergence in the acute phase. However, over time, it is common that spontaneous UBN will transition to DBN, which will be most noticeable in lateral gaze. In the chronic (DBN) phase, another transition from DBN to UBN with convergence may be seen as was the case here. This likely has to do with involvement of the otolithic / translational vestibulo-ocular reflex brainstem pathways, which depend on viewing distance and orbital position. Therefore, vergence often modulates vertical nystagmus causing it to transition acutely and chronically. Spontaneous (chronic) DBN probably has to do with recovery involving the dorsal medullary nucleus of Roller and intercalatus, with lingering damage to the paramedian tracts.