PERIODIC DOWNBEAT NYSTAGMUS

The authors observed a periodic downbeat nystagmus with a cycle of 3 m inutes 30 seconds, beating downward for a period of 90 seconds every 2 minutes. It lasted 86 hours in a patient with severe hypomagnesemia a ssociated with complications from scleroderma. There was no lesion on brain imaging, and an EEG performed during the nystagmus was normal, i ndicating that the most likely explanation for this periodic nystagmus is metabolic. This form of nystagmus may have resulted from severe hy pomagnesemia, possibly associated with thiamine deficiency.