Episodic brainstem compression masquerading as electrodecremental seizures.

An 8-year-old boy developed generalized tonic spasms lasting minutes accompanied by an electrodecremental event on electroencephalogram in association with increased intracranial pressure caused by shunt malfunction. The electroencephalographic abnormalities and clinical attacks occurred despite an otherwise normal neurologic examination, normal initial opening pressure on lumbar puncture and shunt tap, and only mild ventricular dilation revealed by brain imaging. There was no improvement with antiepileptic drugs. Further signs of uncal herniation led to repeat tap of the shunt, revealing a pressure of 800 mm of water. After revision of the shunt "seizures" stopped and the electroencephalogram returned to normal. Antiepileptic drugs were discontinued, with no recurrence of events.