[A case of involuntary movements probably produced by low doses of phenytoin intoxication].

A 49-year-old woman, who presented gait disturbance, orofacial dyskinesia, choreoathetosis and slightly cloudy consciousness, was admitted to our hospital on February 7, 1986. She had a slight fever and sore throat for the previous ten days. She had been treated for hypothyroidism as well as migraine with abnormal electroencephalogram since age 47, and was given a daily dosage of 70 mg phenytoin, 80 mg phenobal, and 125 mg dried thyroid. On admission, she was somnolent, and her speech was slurred. There were choreoathetosis of all extremities, orofacial dyskinesia, horizontal nystagmus, and dysdiadochokinesis with impaired heel-knee and finger-nose test. She could not only walk but also stand by herself. The plasma level of phenytoin was above 40 micrograms/ml (normal: 10 to 20 micrograms/ml). The plasma level of phenobal was normal. T3 was 0.76 ng/dl (normal: 0.96-1.92). T4 was 3.3 micrograms/dl (normal: 5.1-12.8). Biochemical screening, liver and kidney function tests were normal. Cerebrospinal fluid, ECG, chest X-rays and brain CT were normal. Electroencephalogram showed 5 to 6 Hz moderate voltage theta waves with artifacts of electromygram due to orofacial dyskinesia. After phenytoin was discontinued, the dyskinetic movement and gait disturbance disappeared, and her consciousness became alert in parall with reduction of plasma level of phenytoin. We suggested that acute phenytoin intoxication due to low dosages of phenytoin might be precipitated by upper respiratory infection and that involuntary movements in this case might be related to hypothyroidism.