We treated a case of iatrogenic hypermagnesemia that clinically mimick
ed a central brain-stem herniation syndrome. Hypermagnesemia (magnesiu
m level, 9.85 mmol/L [24 mg/dL]) can cause parasympathetic blockade, i
nducing fixed and dilated pupils, in addition to neuromuscular blockad
e. Extreme hypermagnesemia can therefore mimic a midbrain syndrome and
cause a pseudocomatose state.