Progressive medial temporal degeneration with TDP-43 pathology is associated with upper limb and bulbar onset types of amyotrophic lateral sclerosis

Objective This study aimed to clarify the relationship between progressive medial temporal atrophy and onset subtype in patients with amyotrophic lateral sclerosis (ALS). Methods Medial temporal atrophy, ALS functional rating scale (ALSFRS), and cognitive function were assessed in 119 patients who were grouped into three ALS subtypes: bulbar, upper limb, and lower limb onset. Medial temporal atrophy, represented by a Z-score, was determined using an analysis software of magnetic resonance images known as the voxel-based specific regional analysis system for Alzheimer’s disease (VSRAD). Among 119 patients, 60 underwent follow-up VSRAD, ALSFRS, and cognitive testing. The sequential data were compared among onset subtypes. Furthermore, TDP-43 pathology was assessed in 20 autopsied patients (including seven who underwent VSRAD before death) to examine the relationships among medial temporal atrophy, onset subtypes, and severity of the hippocampal TDP-43 pathology. Results Multiple regression analysis revealed that the Z-score at baseline was associated with the age of onset and duration of illness. A high Z-score at baseline and the bulbar/upper limb subtypes affected the progression rate of Z-score. Pathological examination revealed increased hippocampal TDP-43 pathology score associated with bulbar and upper limb subtypes. Moreover, the Z-score before death correlated with the hippocampal TDP-43 pathology score. Conclusion Medial temporal atrophy in ALS is associated with bulbar and upper limb onset subtypes. This progression may be related to the extent of TDP-43 pathology.