Unraveling Shared Pathways: A Comprehensive Systematic Review of Common Fiber Tracts in Amyotrophic Lateral Sclerosis and Frontotemporal Dementia using Diffusion Tensor Imaging

This systematic review evaluated MRI studies of fibre tract abnormalities in patients with amyotrophic lateral sclerosis (ALS) and/or fronto-temporal dementia (FTD). After searching 5 databases, 63 papers met inclusion criteria reporting 1674 patients and 1411 healthy controls. The papers studied a range of fibre tracts. Techniques used included overall comparisons and regions of interest. All papers reported results of fractional anisotropy (FA) and some also reported other DTI metrics. In ALS, the hallmark feature of cortico-spinal tracts (CST) involvement is consistently found, while in FTD the only part of the motor tracts that was found to show changes is the corona radiata (CR). The review also highlighted overlapping abnormalities between ALS and FTD, suggesting that these conditions exist on a spectrum. Both ALS and FTD exhibited CST abnormalities, with extra-motor involvement in the cingulum and the CC. Many tracts including the corpus callosum (CC) and cingulum (Cg), the superior longitudinal fasciculus (SLF) and inferior fronto-occiptal fasciculus (IFOF), were abnormal in both ALS and FTD. The integrity of specific white matter tracts, such as the uncinated fasciculus (uncF), forceps minor, and callosal radiation, appeared critical for cognitive functions related to Theory of Mind, cognitive control, and emotion recognition.There was, however, extramotor involvement in ALS.