A transcranial magnetic stimulation study on Alzheimer's disease and behavioral variant frontotemporal dementia

Abstract

Objective To investigate the changes in cortical excitability and inhibitory circuits of patients with Alzheimer's disease (AD) or behavioral variant frontotemporal dementia (bvFTD) using transcranial magnetic stimulation (TMS). Methods Forty-four patients with AD, 30 patients with bvFTD and 44 healthy controls were enrolled in the study. The epidemiological data of all subjects were collected. Each participant received a neurological evaluation and neuropsychologic tests which included Mini-Mental State Examination (MMSE), Activities of Daily Living (ADL) and Hamilton Rating Scale for Depression (HAMD). Neurophysiological evaluations including resting motor threshold (rMT), active motor threshold (aMT) and cortical silent period (CSP) were conducted by means of TMS. Neurophysiological parameters were compared among groups. Results There were significant differences in MMSE, ADL and HAMD assessments among 3 groups, but no significant differences between AD and bvFTD groups. There were significant changes in left rMT(46.52%±8.77%, 52.00%±7.30% and 52.14%±8.27%, F=6.295, P=0.003), left aMT(29.68%±7.01%, 35.13%±8.46% and 35.39%±7.24%, F=7.735, P=0.001) and right rMT(47.82%±7.94%, 52.07%±8.77% and 53.12%±8.61%, F=4.772, P=0.010) among 3 groups. AD patients showed significantly reduced left rMT and aMT comparing to bvFTD patients (P=0.017 and 0.008 respectively) and controls (P=0.005 and 0.002 respectively). In addition, AD patients had a significant decrease in right rMT comparing to controls (P=0.011). There were no statistically significant differences in TMS parameters between bvFTD patients and controls. Conclusions AD is associated with hyperexcitability of the motor cortex, whereas the lack of changes in motor cortical excitability is found in bvFTD. TMS technique may be helpful in differential diagnosis between AD and bvFTD. Key words: Transcranial magnetic stimulation; Evoked potentials, motor; Alzheimer disease; Frontotemporal dementia