Proton MR spectroscopic imaging in Pelizaeus-Merzbacher disease

Abstract

Background and purpose: Pelizeaus-Merzbacher disease (PMD) is a clinically and molecularly heterogeneous disorder linked to deletion, mutations, or duplication of the proteolipid protein (PLP1) gene locus at Xq22. The current study was conducted to characterize the results of proton MR spectroscopic (MRS) imaging in PMD.

Methods: Three boys with PMD (one with the severe connatal form and two with a more mild clinical phenotype [spastic paraplegia type 2]). and three age-matched healthy control subjects (age range, 2-7 years) underwent MR and MRS imaging. All imaging was performed at 1.5 T. For MRS imaging, oblique-axial sections (thickness, 15 mm; intersection gap, 2.5 mm) were recorded parallel to the anterior commissure-posterior commissure line (TR/TE/NEX, 2300/272/1) with lipid and water suppression. Ratios of metabolite peak areas were calculated, and spectra were bilaterally evaluated.

Results: Diffuse or focal reductions in N-acetylaspartate were observed in the affected white matter in all three cases. These reductions seemed to be consistent with axonal damage. In addition, mild increases in choline and creatine levels were observed; these may have been due to astrocytic changes.

Conclusion: Proton MRS imaging may be helpful in evaluating regional pathophysiologic abnormalities in PMD and in distinguishing PMD from other leukodystrophies, which exhibit different metabolic profiles.

Fig 1.

Regions of interest (squares) in the frontal-lobe white matter, centrum semiovale, and parietal white matter and gray matter were chosen for analysis.

Fig 2.

Severe PMD. T2-weighted MR images (T₂); metabolic images of Cho, Cr and NAA; and selected spectra from the parietal white matter (WM) and parieto-occipital gray matter (GM). T2-weighted MR images show diffuse hyperintensity throughout the white matter, which also has markedly decreased NAA levels. Cho and Cr levels are also mildly elevated in the centrum semiovale. Gray matter spectra also show a lower ratio of NAA/Cho and NAA/Cr in the patient compared with that in the control subject. A, Patient 1, aged 2 years 5 months. B, Control subject 1, aged 1 year 9 months.

Fig 3.

Mild PMD. T2-weighted MR imaging; metabolic images of Cho, Cr, and NAA; and selected spectra from the parietal white matter and parieto-occipital gray matter. T2-weighted MR images show patchy hyperintensity with greatest involvement in the centrum semiovale. NAA levels are bilaterally decreased in the parietal white matter. Gray-matter spectra are normal. A, Patient 2, aged 3 years 8 months. B, Control subject 2, aged 3 year 2 months.