We experienced a case of brainstem infarction caused by protein S （PS） deficiency with oral paresthesia as the initial symptom. The patient was a 27-year-old woman with a history of smoking. Initially she realized numbness in the left half of her tongue. As the patient complained of not only hypoesthesia in the oral cavity and left half of the face, but also discomfort in the left upper extremity, cranial nerve disease was suspected. She was referred to the department of neurology. MRI revealed a small lesion on the left dorsal side of the pons, and demyelinating disease was suspected. Although steroid pulse therapy was initiated, the symptoms did not improve. However, on the basis of the repeated MRI result, a pontine infarction was suspected. The paresthesia was gradually improved by pharmacotherapy. During this time, decreased PS level was found and it was determined that she had been taking low-dose pills. This medication was immediately discontinued. The low PS level slowly improved after discharge. On the basis of these findings, we supposed that the onset of brainstem infarction in the present case was due to the acquired PS deficiency caused by multiple factors including low-dose pills and smoking.
