Diffusion-weighted imaging and proton MR spectroscopy of white matter abnormalities in a case of phenylketonuria

Phenylketonuria (PKU) is the most common congenital disorder of amino acid metabolism. We report diffusion-weighted imaging (DWI) and proton magnetic resonance (MRI) spectroscopy findings of white matter abnormalities in a 22-year-old woman with phenylketonuria. MRI demonstrated extensive abnormal signal changes in the periventricular white matter of cerebral hemispheres bilaterally. True restricted diffusion of water was identified in the corresponding abnormal white matter regions on DWI. Proton MR spectroscopy revealed mildly increased choline/creatine ratio, while the N-acetyl-l-aspartate/creatine ratio was normal. There was no phenylalanine peak at 3.80 and 7.36 ppm. The findings were most likely consistent with active inflammatory process causing progressive white matter degeneration.