Accuracy of Conventional MRI in ALS

Background: There is currently no definite neuroimaging test to detect amyotrophic lateral sclerosis (ALS), which leads to significant delay in diagnosis, particularly if one takes into account the rapidity of disease evolution. Hyperintensity of the corticospinal tracts (CST) on T2 or fluid-attenuated inversion recovery (FLAIR) weighted magnetic resonance imaging (MRI) has been well described, but data on sensitivity and specificity in larger series is lacking to help guide its application to clinical care. Methods: We analyzed clinical and MRI data from 64 patients with a definite retrospective diagnosis of ALS. In this case-control study, two experienced blinded neuroradiologists systematically assessed defined rostrocaudal segments of the intracranial course of the CST. Results: The overall sensitivity and specificity of conventional MRI for the diagnosis of ALS were 48% and 76% respectively. Highest specificities for CST hyperintensity were noted for the subcortical white matter (92%), centrum semiovale (88%) and medullary pyramids (92%). The lowest specificities were found for the cerebral peduncle (36%) and internal capsule (32%). We did not find a correlation with the rate of clinical progression, age of onset or the presence of upper motor neuron signs on examination. Conclusion: Conventional MRI was not found to be a reliable diagnostic tool for ALS and it did not help predict clinical characteristics such as speed of evolution or prominence of upper motor neuron signs. Its main role in the setting of ALS should remain to help exclude alternative diagnostic considerations. A multimodal approach relying on newer functional and structural MRI techniques still needs to be developed and validated.