Acute phenytoin toxicity mimicking stroke following cardiopulmonary bypass

Abstract

A 55-year-old diabetic, hypertensive and dyslipidemic male with functional class III angina was admitted for coronary revascularization. Patient had a history of stroke with left hemiparesis five years ago, with complete recovery within a year. He had one episode of seizure three years back but did not seek any medical advice. Cardiac evaluation revealed triple vessel disease with fair left ventricular function without any intracardiac clots. Liver function test revealed SGOT of 48 u/L and SGPT of 56 u/L (normal range up to 40 u/l). Ultrasonography of abdomen showed fatty liver. Carotid artery duplex scanning showed 30% stenosis of right and 45% stenosis of left internal carotid artery. Computerised tomography (CT) of brain revealed chronic infarct in right frontal and gangliocapsular region. Electroencephalogram three weeks prior to surgery showed a spike and wave discharge over temporal areas consistent with seizure disorder, and patient was started on oral Phenytoin 100 mg thrice daily. He underwent coronary artery bypass grafting under CPB. Postoperatively hemodynamics remained stable. Oral aspirin and Phenytoin were restarted on first postoperative day. He was initially in a state of confusion, and, on the 3rd postoperative day, developed pronounced ataxia, nystagmus, dysarthria and vomiting. A likely clinical diagnosis of posterior circulation stroke was considered. CT scan ruled out a hemorrhagic stroke but could not rule out new embolic phenomena. Heparin infusion was thus started empirically. The neurological status was slowly deteriorating. MRI done on the fifth postoperative day revealed no fresh structural lesions in the brain. At this stage a likely possibility of Phenytoin toxicity was considered. Serum total Phenytoin concentration estimation revealed a toxic level of 40 microgram/ deciliter. (Therapeutic range 10-20 mcg/dl) which clinched the diagnosis. Patient also had hyponatremia requiring frequent corrections, however levels of urinary sodium were low. Phenytoin was stopped and patient showed good recovery with no residual neurological deficit within 15 days. At discharge his serum Phenytoin level was within normal range and he was advised to remain under a neurologist follow up.