Different TMS patterns of intracortical inhibition in early onset Alzheimer dementia and frontotemporal dementia

Objective: To investigate putative changes in cortical excitability of patients affected by early-onset mild dementia by means oftranscranial magnetic stimulation (TMS) and to verify whether a peculiar neurophysiological profile may contribute to characteriseAlzheimer’s disease (AD) vs frontotemporal dementia (FTD).Methods: Motor threshold and intracortical inhibition (ICI) and facilitation (ICF) after paired-pulse TMS (inter-stimulus intervals from 1to 20 ms) were studied in two groups of early-onset demented patients with a neuropsychological profile suggestive of ADðn¼12Þand FTDðn¼8Þ:Twelve age-matched healthy subjects were considered as control group. In both patient groups, recordings were performed beforeand after a single oral dose of 4 mg galantamine.Results: No significant difference in motor threshold was observed among the three studied groups. On the contrary, early-onset ADshowed a significant reduction of ICI compared to control group, no changes were detected in FTD patients. No significant changes in ICFwere found between both patient groups and healthy subjects. The acute administration of galantamine reversed the modified ICI in ADgroup.Conclusions: The differential pattern of ICI exhibited by early-onset AD vs FTD in the early stage of disease may represent a non-invasive, reproducible electrophysiological tool, which may contribute to early differential diagnosis and, possibly, to monitor therapeuticeffectiveness.Significance: The present results support the possibility that subtle, early modifications in intracortical circuitry features AD, but not FTDpatient