Introduction: Currently, we use brain MRI quantitative susceptibility mapping analysis (QSM) to examine susceptibility in the motor cortex, correlating with iron deposition, which is typically increased in motor neuron disease. Familial ALS is most commonly due to the C9ORF72 and SOD1 genes. Pathology studies have demonstrated more protein aggregates in the cerebellum and temporal lobes in C9ORF72 ALS, and more protein aggregates in the frontal and temporal lobes in SOD1 ALS. Other means of looking for protein are not established. We designed a study to retrospectively assess the MRI/QSM correlation with motor neuron disease severity, as measured by MRC, FVC, El Escorial criteria and ALSFRS-R. We also looked for regional changes in genetic ALS patients.
Methods: We retrospectively reviewed the charts of all motor neuron disease patients seen in Neurology at Hospital for Special Surgery from 2013 through 2018 who had MRI with QSM. One neuroradiologist examined the scans and quantified relative susceptibility. We collected values for ALSFRS-R, FVC, El Escorial diagnosis, and sum of MRC, where documented.
Results: Although there is a significant difference between patients with Definite ALS by El Escorial criteria (43.8 ppb) and ‘normal,’ QSM failed to correlate with ALSFRS-R, FVC, or sum of MRC. Further, we found no distinguishing abnormalities in the brain MRIs of the genetic ALS patients reviewed. QSM of the motor cortices and corticospinal tracts showed qualitative increase in susceptibility, which is not unique to type of ALS.
Discussion: MRI/QSM may not be useful in distinguishing ALS patients by severity or mutation. It may be useful to distinguish ALS from mimic syndromes. This could be because the amount of protein aggregation may not be directly related to axonal loss, or that it affects certain neurons/ tracts more than others.