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Imaging Bio markers of ALS

A number of studies in ALS patients have shown that magnetic resonance spectroscopy (MRS) and diffusion tensor (DT)-MRI can detect corticospinal lesions. MRS reveals reduction of N acetyl aspartate (NAA), a biomarker of neuronal integrity.

In ALS, decreased NAA is not only restricted to the motor cortex and corticospinal tract, but is also observed in premotor regions, the primary sensory cortex, and extramotor frontal regions with relative sparing of the parietal lobe. However, because of their relative lack of sensitivity and specificity, these techniques are currently inadequate for use as diagnostic tools in individual patients.

DT-MRI reveals the structure of nerve fibers in the corticospinal tract that correlates with function, thus revealing the ALS pathology. DT tractography enables visualization and evaluation of corticospinal and corticobulbar tract dysfunction in patients with ALS. In vivo DT-MRI measures demonstrate differences in white matter degeneration between sporadic ALS and a unique familial form of the disease, indicating that genotype influences the distribution of cerebral pathologic features in ALS (Stanton et al. 2009). Functional MRI (fMRI) reveals a general pattern of cortical reorganization for motor function in patients with ALS when compared with that seen in normal subjects.

In spite of limitations, imaging modalities provide insight into the pathophysiological process in ALS and may play a role in accurate identification of upper motor neuron pathology in ALS. Further investigations are needed to determine and to compare the relative usefulness of various neuroimaging techniques (Wang et al. 2011).

 
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