An 81-year-old woman presented to the emergency room because of coma while sleeping. She was recently diagnosed with diabetes and had been treated with solely metformin therapy.
Her fingerprick blood glucose level was 1.3mmol/L. Head CT-scan and CTA were normal. Her blood glucose level was rapidly normalized by hypertonic glucose solution infusion but her consciousness did not improve. The most likely diagnosis was hypoglycemic encephalopathy.
This weird ocular movement is called short-cycle periodic alternating gaze or ping-pong gaze. This finding usually indicates bilateral cerebral damage (e.g., bilateral cerebral infarcts) with an intact brainstem, but it has also been described with posterior fossa hemorrhage, basal ganglia infarcts, hydrocephalus, and overdose of the monoamine oxidase inhibitor tranylcypromine. The disorder may occasionally occur in coma with no structural hemispheric lesion like in this case.
Brazis, P. W., Masdeu, J. C., & Biller, J. (2012). Localization in clinical neurology. Lippincott Williams & Wilkins.