T51. TMS evaluation in cognitive impaired patients according to new criteria for AD

Introduction Alzheimer‘s disease (AD) is characterized by loss of synaptic connections, cell death and disruption of structural and functional networks. One of the most consistent findings is the impairment of cortical plasticity, especially Long Term Potentiation (LTP) mechanisms. Recently, the use of a new lexicon and new diagnostic criteria allowed to considered AD as a clinico-biological entity identifiable in vivo on the presence of biomarkers. In light of the new lexicon and the new diagnostic criteria, aim of the current work is to investigate cortical plasticity in cognitive impaired (CI) patients admitted for the first time in the memory clinic and stratified according to CSF biomarker profile; moreover we followed patients up to a period of three years to explore the relationship between neurophysiological, neuropsychological and CSF biomarker and clinical progression. Methods Seventy-one consecutive patients recruited at the memory clinic admitted for their first visit for complaining memory symptoms and underwent CSF sampling. Then they undertake TMS examination, investigating mechanisms of long term potentiation (LTP) with intermittent Theta Busrt Stimluation (iTBS) and intracortical circuits. Patients were followed longitudinally with MMSE testing up to 36 months. According to the new criteria AD proposed we divided CI patients in basis of evidence ofin vivobiomarkers (as assessed by CSF analysis) and the presence of dementia. Resulting in three groups: (1) Mild Cognitive Impaired (MCI) patients (n = 22); Prodromal AD (PROAD) patients (n = 25); AD Dementia (ADD) patients (n = 25). Univariate regression analyses were performed to characterize the association between each clinical and neurophysiological variable with clinical progression (delta MMSE score at 36 months respect to baseline). A control group of 23 healthy subjects (HS) was recruited for control. Results For neurophysiological evaluations only iTBS protocol was different among the different groups showing a paradoxical reversal of LTP for ADD and PROAD and a poor response for MCI patients. ProAD worsened faster than MCI. Regression analyses showed that LTP impairment was related to clinical progression. Kaplan-Meyer analyses showed that CI patients expressing the worst LTP values were the ones to progress faster in a 3 year time. Conclusion the new criteria based on the presence of biomarkers and dementia allow us to identify CI patients at a prodromal stage that will develop dementia due to AD. LTP impairment drives the clinical progression in CI patients at prodromal stages even without evidence of biomarker positivity, confirming its pivotal role in determining cognitive decline.