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.