High T2 Signal in Primary Lateral Sclerosis Supports the Topographic Distribution of Fibers in the Corpus Callosum: Assessing Disease in the Primary Motor Segment

SUMMARY: PLS is a disease of the UMN, distinguished from ALS in prognosis and absence of LMN signs. We present, to our knowledge, the first conventional MR imaging visualization of the callosal motor segment, a concept previously supported by primate models, electrophysiologic studies, and postmortem examinations. Modification of the Witelson topographic scheme of the CC is supported by MR tractography. On the basis of 2 cases of PLS, we present conventional imaging confirmation of the revised topographic scheme of fiber distribution across the CC. ALS : amyotrophic lateral sclerosis CC : corpus callosum CST : corticospinal tract DTI : diffusion tensor imaging FA : fractional anisotropy FLAIR : fluid-attenuated inversion recovery LMN : lower motor neuron PLS : primary lateral sclerosis UMN : upper motor neuron