Pseudonormalization on diffusion-weighted MRI: An ominous sign in Leigh syndrome

Abstract

We serially investigated the clinical course, T1- or T2-weighted magnetic resonance imaging (MRI), and diffusion-weighted imaging (DWI) features in a patient with Leigh syndrome. In the early phase, DWI sensitivity for detection of the lesions was similar to that of T1- or T2-weighted MRI. In the chronic phase, however, signals showed a discrepancy between DWI and T1- or T2-weighted images. The T2 hyperintensity persisted and showed no changes during his clinical regression. In contrast, the signals on DWI returned to normal (isointensity). In the medulla oblongata, the apparent diffusion coefficient (ADC) values in the affected areas (0.63 and 0.59 x 10⁻³ mm²/s) were lower than those of the unaffected area (0.78 ± 0.04 and 0.76 ± 0.05 x 10⁻³ mm²/s) at 14 and 16 months. In contrast, at 25 months of age, the ADC value in the affected area (0.87 x 10⁻³ mm²/s) was slightly higher than those of the unaffected area (0.75 ± 0.03 x 10⁻³ mm²/s). These findings may reflect the pseudonormalization, which is considered to reflect pathologic changes of progressive gliosis and decreased neuronal density. Serial DWI studies may be useful not only for initial diagnosis, but also for reconsideration of pathophysiologic changes of lesions in Leigh syndrome.

Keywords

Leigh syndrome - diffusion-weighted imaging - pseudonormalization - apparent diffusion coefficient