Unraveling pathology in juvenile Alexander disease: serial quantitative MR imaging and spectroscopy of white matter.

[alexander disease]

Alexander disease is a rare disorder of the central nervous system with characteristic symmetric white matter abnormalities with frontal predominance on magnetic resonance (MR ) images . Histopathology shows a lack of myelin in the affected white matter , variably interpreted as hypomyelination or demyelination . To increase our insight into the nature of the pathology leading to the MR imaging findings in Alexander disease , we applied serial MR imaging , spectroscopy , magnetization transfer (MT ) imaging (MTI ), and diffusion tensor imaging (DTI ) in six patients with juvenile Alexander disease .The MR imaging protocol comprised T 1 - and T 2 -weighted spin echo images and fluid-attenuated inversion recovery images . Fractional anisotropy (FA ), apparent diffusion coefficient (ADC ), and MT ratio (MTR ) maps were generated , and MR spectroscopy concentrations were quantified for several metabolites .MR imaging showed similar cerebral white matter abnormalities in all patients , with only minor increase on prolonged follow-up , despite sometimes serious clinical progression . MR spectroscopy showed highly elevated levels of myo-inositol , lactate , and choline-containing compounds and decreased total N-acetyl-aspartate and N-acetyl-aspartyl-glutamate levels in the abnormal white matter . High values of ADC were observed , and both FA and MTR were attenuated .The sequential MR imaging findings in Alexander disease provide strong evidence against active demyelination as sole explanation for the underlying pathology . An alternative explanation for our spectroscopic , DTI , and MTI findings-which would suggest demyelination -could be hyperplasia and hypertrophy of astrocytes , as seen in low grade gliomas .

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