Lidocaine‐Dependent Early Infantile Epileptic Encephalopathy with Hyponatremia and Highly Suppressed EEG
Authors: Sawaishi Yukio , Yano Tamami , Enoki Masamichi , Takada Goro 
Published: August 2005

Purpose: Early infantile epileptic encephaiopathy with suppression burst (EIEE) is characterized by an EEG pattern that alternates between an irregular mixture of spikes and waves and almost flat activity, each lasting from 1 to several seconds. This report presents a case characterized by lidocaine dependence, intractable hyponatremia, and an EEG pattern that alternates between extremely long suppression and short burst. In addition, the possible pathomechanism of the suppression is discussed.

Case report; We examined a female patient born at term by normal delivery, who had a birth weight of 2,546 g and a head circumference of 33 cm. She did not present with asphyxia but hardly cried artd was unable to breast feed. Blood studies showed persistent hyponatremia ranging between 120 and 130 mEq/L. Endocrinological examinations disclosed no abnormalities. Despite NaCl loading and water restriction, the persistent hyponatremia did not show improvement. Tube feeding was started, but her activity and responsiveness remained poor. One month after birth, clonic seizures were observed in the face and limbs. Phenobarbital and diazepam were only transiently effective. Valproate and vitamin B6 were ineffective. Ten days after the onset of seizures, the patient was transferred to our hospital. On admission, she demonstrated repeated seizure activity every 1 to 2 minutes, lasting 10 to 15 seconds. Movement consisted of a series of tonic extension of the upper limbs, head turning toward the right, and clonic right hemiconvulsion. The head circumference increased to 41 cm at one and half month. The EEG showed burst activity during the seizure movements and suppressed flat activity during the interictal phase lasting I to 2 minutes. There were no spontaneous movements other than seizure and no response even to noxious stimuli. After starting intravenous lidocaine administration, the seizure activity improved and completely disappeared within 8 hours. The next day, the patient was able to cry and her hyponatremia improved. Three days after starting lidocaine, she was able to breast feed and the duration of the suppression phase in the EEG decreased to less than 10 seconds. Within several hours of ceasing lidocaine administration, the seizure movements reappeared and the EEG showed an extremely suppressed pattern. Within a several hours after restarting lidocaine, seizure movements disappeared, and the EEG improved. Based on these observations, we continued intravenous administration of lidocaine at a serum concentration of approximately 0.5 y/ml. Thereafter, head circumference improved, the EEG changed from a suppression burst pattern to an irregular slow wave pattern, and the patient showed more development, Nevertheless, an MRI revealed progressive cerebral atrophy. We changed from intravenous administration of lidocaine to the viscous lidocaine to enable administration through a gastric tube.

Given the pharmacological mechanisms of lidocaine as a sodium channel blocker, we speculate that our patient had a sodium channel dysfunction that caused an overflow of sodium from the extracellular apace into neurons and other excitable cells. This hypothesis could explain the characteristic findings in our patient including intractable hyponatremia, extremely suppressed EEG, and subacute megalencephaly. We believe that this mechanisms merits further consideration.