Transcranial Magnetic Stimulation as a Diagnostic Tool in Mild Cognitive Impairment: A Systematic Review

Background/Objective: Mild cognitive impairment (MCI) often represents the prodromal stage of neurodegenerative dementia. Identification of Alzheimer disease (AD) and other dementias in the MCI stage is essential for early intervention. Transcranial magnetic stimulation (TMS) has gained interest as a non-invasive method to evaluate cortical excitability and neurotransmitter function. This systematic review aims to evaluate the diagnostic utility of TMS-derived indices, such as short-latency afferent inhibition (SAI), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and long-interval intracortical inhibition (LICI) in MCI populations. Methods: Following PRISMA guidelines, 14 studies were selected, encompassing 476 MCI patients. Reported outcomes related to TMS measures (SAI, SICI, ICF, LICI) were reviewed across various MCI phenotypes. Results: Most studies report reduced SAI, a marker of cholinergic dysfunction, in amnestic MCI and MCI due to AD. Alterations in SICI and ICF, markers of GABAergic and glutamatergic dysfunction, were more variable, mainly observed in MCI of non-AD type. LICI showed no consistent changes. One study demonstrated increased clinicians' diagnostic confidence when TMS data were incorporated. Conclusions: TMS measures hold promise as a non-invasive tool for early and differential diagnosis of MCI. Further standardized and longitudinal research is needed to confirm its clinical applicability.