Periodic downbeat nystagmus.

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

Monocular central dazzle after thalamic infarcts.

The authors observed a patient after he had ischemic strokes in both paramedian thalamic regions, which were more marked on the left side. Symptoms included dysphasia, vertical binocular diplopia, right-sided hemianopia, and a right-sided sensory and motor deficit, sparing the face. However, the most disturbing phenomenon was a painless, left monocular dazzle, which was the presenting symptom and also the only persisting symptom. This report shows that a thalamic lesion may be at the origin of central dazzle, and to the authors' knowledge, it is the first clinical observation of its monocular occurrence. It is conceivable that this dazzle was due to optic-trigeminal summation