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Diffusion-weighted MR Imaging in Patients with Phenylketonuria: Relationship between Serum Phenylalanine Levels and ADC Values in Cerebral White Matter¹

¹ From the Departments of Radiology (K.K., K.N., S.M., N.O., H.Y., Y.I.) and Pediatrics (Y.O., Y.H.), Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi, abeno-ku, Osaka 545-8585, Japan. Received April 6, 2004; revision requested June 15; revision received August 24; accepted October 4. Address correspondence to K.K.

PURPOSE: To prospectively determine the relationship between serum phenylalanine levels and apparent diffusion coefficient (ADC) values in the cerebral white matter of patients with phenylketonuria (PKU).

MATERIALS AND METHODS: Institutional review board approval was obtained, and participants provided informed consent. Magnetic resonance (MR) imaging, which included T1- and T2-weighted, fluid-attenuated inversion-recovery (FLAIR), and diffusion-weighted examinations, was performed in 21 patients with PKU (nine male and 12 female patients; age range, 3–44 years; mean age, 19.4 years). ADC values in deep cerebral white matter were calculated for each patient. Serum phenylalanine levels were obtained in all patients within 12 days after MR imaging. Serum phenylalanine levels were measured in 16 patients 1 year before MR imaging. ADC values in cerebral white matter and serum phenylalanine levels were compared. A total of 21 control subjects (12 male and nine female patients; age range, 3–33 years; mean age, 20.6 years) underwent MR imaging. ADC values in cerebral white matter were compared with serum phenylalanine levels by using the Pearson correlation.

RESULTS: Abnormal high signal intensity in white matter on T2-weighted and FLAIR MR images was noted in patients with PKU who had serum phenylalanine levels of more than 8.5 mg/dL (514.2 µmol/L). Diffusion in posterior deep cerebral white matter tended to be restricted in patients when increased serum phenylalanine levels were measured after MR imaging (r = –0.62). There was a correlation between ADC values in posterior cerebral white matter and serum phenylalanine levels measured 1 year before MR imaging (r = –0.77). ADCs of control subjects were significantly higher than ADCs of patients with PKU (P < .005).

CONCLUSION: Posterior deep white matter in patients with PKU and a serum phenylalanine level of more than 8.5 mg/dL showed high signal intensity in white matter on T2-weighted and FLAIR MR images and revealed decreased ADC. We suggest that to avoid brain-restricted diffusion due to hyperphenylalanemia, patients with PKU should maintain serum phenylalanine levels of less than 8.5 mg/dL (514.2 µmol/L).

© RSNA, 2005

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