44-year-old woman with history of bipolar disorder on valproic acid, and LTG, presented with ‘bouncy vision’, sensation of ‘room spinning’, and tinnitus described as ’sounds of the ocean’. At her first ED visit, Head CT - unremarkable, MRI brain (without contrast) - nonspecific subcortical white matter changes. Valproic acid and LTG levels were 76 and 19 mcg/ml respectively. She was discharged with provisional diagnosis of Peripheral Vertigo and LTG dose was decreased, which was increased two months prior by her psychiatrist.
On her third ED visit, neurology was consulted, a complete neurological examination revealed DBN in primary gaze, left and right gaze, and downgaze. The nystagmus improved in upgaze. She also had bilateral upper extremity dysmetria on finger to nose with staggering gait. She was admitted for suspected LTG toxicity (serum LTG: 23·6 mcg/mL). LTG was discontinued and her symptoms resolved completely the next day. On follow-up she had normal neurological examination with no residual symptoms.