PRIMARY POSITION UPBEAT NYSTAGMUS WITH SPECIAL REFERENCE TO ALTERATION TO DOWNBEAT NYSTAGMUS

A 24-year-old man was admitted to the University Hospital showing seve re dehydration that might have been the result of medicine-induced gas tritis. Wernicke's encephalopathy was suspected in this patient. On ad mission, primary position upbeat nystagmus (PPUN) was found. The patie nt showed tongue fasciculation and loss of gag reflex, which, however, soon returned to normal. Electronystagmographic (ENG) findings were s uggestive of lesions in the brainstem. Based on neurological signs and symptoms, we concluded caudal brainstem lesions might be a possible s ite responsible for the upbeat nystagmus. This nystagmus, however, was later found to be reversed to downbeat nystagmus. This is considered to have been due to predominant differences in vertical velocity which are induced by gravity.