Neuropediatrics 2005; 36 - P55
DOI: 10.1055/s-2005-868040

Pyridoxine-responsive seizures in a patient with infantile hypophosphatasia

E Haberlandt 1, W Högler 1, S Scholl-Bürgi 1, S Foerster 1, D Karall 1, K Kapellari 1, S Baumgartner 1
  • 1Medizinische Universität Innsbruck, Klinische Abteilung für allgemeine Pädiatrie, Innsbruck, Österreich

Hypophosphatasia is a rare autosomal dominantly inherited disease, with low alcaline phophatase activity as a hallmark. Typically, patients have rickets with reduced alcaline phosphatase activity in serum and an elevated concentration of phosphoetholamine in urine. Four types exist (fetal, infantile, juvenile and adult), with more serious and poorer prognosis the younger the patients at onset. The simultaneous occurence of pyridoxine- or pyridoxalphosphate-responsive seizures has only been described in two cases so far.

We report a seven-month-old patient with cerebral seizures. Perinatal history was uneventful. At the 7th day of life series of myoclonic and tonic seizures became apparent. Seizures could be interrupted by diazepam, but were therapy resistent against phenobarbital on long term. EEG showed continuous suppression-burst activity. Administration of 2×100mg pyridoxine i.v. did not show any change in EEG activity, but clinically seizures were immediately stopped. A transitory respiratory depression was interpreted as a side effect of pyridoxine. A few days after pyridoxine administration a normal background activity could be seen in EEG, the patient was seizure-free with oral maintenancy of pyridoxine (10mg/kg/d). The child showed a nearly normal cerebral development with only slight hints of developmental retardation. A progressive dystrophy and rachitic bone manifestations became apparent with time, and hypophophatasia was diagnosed through markedly decreased activity of alcaline phosphatase in serum.

It is very unusual and only reported twice so far that pyridoxine-responsive seizures occur simultaneously with hypophosphatasia. We conclude that in any case of pyridoxine-responsive seizures in children an alcaline phosphatase activity in serum should be measured to exclude hypophosphatasia. Cases like this could provide new insight about pyridoxine-responsive seizures, their neurometabolic background and epileptogenic significance.