Specific Imaging Findings. Metachromatic leukodystrophy (MLD) is a classical leukodystrophy with initially pure white matter involvement. Hyperintense T2 signal of supratentorial white matter with sparing of the subcortical white matter is typical, at least in the initial stages. The “tigroid” pattern is a peculiar radial stripe appearance within the centrum semiovale due to sparing of perivascular myelin around transmedullary vessels – this finding is strongly suggestive of MLD. The imaging appearance varies over time with a progressive posterior–anterior and centrifugal gradient of white matter involvement. The brainstem and cerebellum are spared until the very late stages. The abnormal white matter does not enhance with contrast; however diffuse enhancement of cranial nerves and cauda equina is typically present. DWI may show a tigroid pattern and more diffuse hyperintense abnormalities, without consistent reduction in ADC values, likely representing a combination of T2-shine through and truly reduced diffusion. Thalamic T2 hypointensity frequently develops over time. MR spectroscopy is nonspecific, with decreased NAA, increased myoinositol, and presence of lactate; NAA levels correlate with motor function. Pertinent Clinical Information. There are several clinical phenotypes of MLD according to the age of onset, with the late infantile form accounting for 70% of cases. In this form, patients present between 6 months and 3 years of age with hypotonia, dysarthria, ataxia, unsteady gait and progressive loss of motor skills. They develop peripheral neuropathy, which may be painful, optic atrophy, and become paraplegic and later quadriplegic. Decerebration and demise occur between 3 and 6 years of the onset.
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