Neglected Atypical Pyridoxine Dependent Seizures

Omid Yaghini, MD; Mohammad-Amir Shahkarami*, MD; Somayeh Shamsaii, MD Pediatrics Department, Isfahan University of Medical Sciences, Isfahan, IR Iran Received: Nov 02, 2009; Accepted: Mar 13, 2010 Vitamin B6 (pyridoxine) dependent seizure (PDS) is an autosomal-recessively inherited disorder which starts within a few hours of birth or even earlier, and can cause intrauterine seizures[1,2]. It occurs while the serum level of B6 vitamin is normal. It is the result of a defect in pyridoxine binding to its apoenzyme glutamate decarboxylase which finally leads to reduced concentrations of Gamma-aminobutyric acid (GABA). Low concentration of GABA is related to decreased seizure threshold[3]. The frequency of PDS is unknown and limited cases have been reported worldwide[4]. Some cases from Iran have already been reported too[5]. Typical PDS is diagnosed according to the following criteria described by Baxter: 1) Seizures resistant to traditional antiepileptic treatment 2) Cessation of seizures with pyridoxine administration, 3) Complete seizure control on pyridoxine monotherapy 4) Recurrence of seizures upon pyridoxine withdrawal[6]. Patients with atypical forms of PDS are more frequently reported than those with classic forms. Atypical PDS must be highly noted regarding the following specifications: 1) Initial response to anticonvulsants 2) No recurrence of attacks even after 6 weeks of pyridoxine or anticonvulsant discontinuation 3) Initial failure of response to pyridoxine in the first 8 months of life. These items lead to delayed diagnosis of atypical PDS. This was the case in our following patients. Case 1: This 6-month-old girl was admitted to emergency room of pediatrics department of Alzahra hospital in Isfahan with status epilepticus and hypothermia. The patient had recurrent tonic seizures since she was 1 month old. She was the third child of a family with three chilren. Her parents were not related, no family history of epilepsy or any other type of seizure was present. The other two children were healthy. Pregnancy and delivery was uneventful. Birth weight 3000 grams. Her development was delayed. With anti-epileptic drugs like phenytoin, phenobarbital and clobasam in full therapeutic dosage the seizures were temporarily controlled during several previous hospitalizations in other centers but recurred every time after discharge from hospital. EEG showed sharp waves, brain CT scan was normal. At admission, all laboratory tests were normal. Metabolic tests, amino acid chromatography with BALL method, plasma ammoniac and blood gas were normal. After admission, 100 mg intravenous vitamin B6 was given as loading dose, continued by 40mg per day orally. After 3 days, she was discharged without any seizure recurrence. Other antiepileptic drugs were gradually tapered. Under continued pyridoxine monotherapy she became completely seizure free, and at the age of 6 years she went to school with normal mental development and normal EEG. Case 2: This patient was a 4-month-old girl, the second child of healthy unrelated parents, delivered after a normal term pregnancy by cesarean section. Birth weight was normal. No family history of epilepsy or any other type of seizure. The patient was frequently admitted to our hospital for intractable seizures: tonic seizures with upward gaze that began on 12th Letter to Editor Iran J Pediatr Dec 2010; Vol 20 (No 4), Pp: 498-501