Electrophysiological differences in cortical excitability in different forms of dementia: A transcranial magnetic stimulation and laboratory biomarkers study

Background. - The aim of the present study was to identify neurophysiologic markers to differentiate between Alzheimer dementia (AD), Vascular dementia (VaD), and Parkinson's disease dementia (POD), and to examine their relationship to levels of transforming growth factor beta 1 (TGF beta 1). Methods. - The study included 15 patients with each type of dementia (AD, VaD, PDD) and control subjects. Dementia patients were diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders 4th edition-revised (DSM-W-R). Modified Mini Mental State Examination (MMMSE), motor cortex excitability including resting and active motor thresholds (rMT, aMT), input-output (I/O) curve, contralateral and ipsilateral silent periods (cSP, iSP), short-interval intracortical inhibition (SICI) at 1,2 and 4ms, and serum levels of TGF beta 1 were examined. Results. - There were no significant differences between groups with regards to age, sex, education or socioeconomic level. There was significant neuronal hyperexcitability in the form of reduced rMT and aMT and a shallower I/O curve in all three groups of dementia compared with the control group. The durations of cSP and iSP were longer in AD and PDD groups compared with the control group, whereas there were no significant differences in VaD. SICI was less effective in the three dementia groups than in the control group at intervals of 4ms. Serum levels of TGF beta 1 were significantly elevated in all dementia groups in comparison with the control group. There was a significant negative correlation between serum level of TGF beta 1 and cSP, iSP, and SICI across all patients and a significant negative correlation between serum level of TGF beta 1 and iSP duration in AD. Conclusion. - Although motor thresholds were reduced in all patients, measures of SICI, cSP and iSP could distinguish between dementia groups. Serum level of TGF beta 1 negatively correlated with iSP specifically in the AD group. This suggests that levels of TGF beta 1 may relate to GABAergic dysfunction in dementia. (C) 2020 Elsevier Masson SAS. All rights reserved.