Malignant hyperphenylalaninemia: CT and MR of the brain.

A defect in biopterin synthesis not only prevents the transformation of phenylalanine to tyrosine (as in classical phenylketonuria, PKU) but also blocks the biosynthesis of the neurotransmitters dopamine, norepinephrine, and serotonin, causing severe neurologic disturbances. The brain CT and MR findings in this rare disorder have not been described. In the present series, eight patients with PKU were all examined with CT, three were also examined with MR imaging. In spite of severe clinical findings, CT was normal or almost normal in three patients; in three other children, moderate loss of brain volume was found. White matter disease was found in three patients (moderate in two and severe in one) and was also found in an additional patient with classical PKU. PKU should therefore be added to the list of possible causes for white matter disease. Furthermore, biopterin-dependent PKU should be considered when the CT examination in a child with severe neurologic manifestation only shows discrete pathology.