Patients with ALS, characterized by motor system degeneration, can also develop cognitive and/or behavioural symptoms that lie on a continuum with the behavioral variant of frontotemporal dementia (bvFTD).

Eighty-three ALS, 35 bvFTD and 61 controls underwent clinical/cognitive evaluations and MRI scan. ALS patients were classified in 54 ALS pure-motor (ALSpm), 21 ALS with cognitive/behavioural impairment (ALSci/bi) and 8 ALS with FTD (ALS-FTD). The structural value of the brain connections was considered and normalized relative to controls. Statistical distribution analysis was performed to identify structural patterns between bvFTD and ALSpm and to assess ALS-like or a bvFTD-like patterns in ALSci/bi and ALS-FTD.

Compared to ALSpm, bvFTD showed greater structural involvement of the connections within and between frontal, temporal and parietal lobes. Conversely, ALSpm patients showed greater involvement of the connections between sensorimotor and basal ganglia areas, compared with bvFTD. ALSci/bi and ALS-FTD showed an ALSpm-like pattern within sensorimotor and basal ganglia areas. Within the frontotemporoparietal networks ALSci/bi and ALS-FTD behaved differently: ALSci/bi showed a bvFTD-like pattern only within the parietotemporal connections, while ALS-FTD showed a bvFTD-like pattern also within frontal and between frontal and sensorimotor areas.

This study showed a widespread structural damage in bvFTD, particularly in the connections within frontotemporal areas and between frontal and other lobes, and a more focal structural damage within sensorimotor-basal ganglia areas in ALSpm. ALSci/bi and ALS-FTD showed an ALS-like pattern with the exception of a greater damage within the frontal and parietotemporal areas, signature of the occurrence of cognitive impairment.