Parkinsonism is associated with altered primary motor cortex plasticity in frontotemporal dementia-primary progressive aphasia variant

In frontotemporal dementia (FTD), the behavioral variant (bv-FTD) and nonfluent variant of primary progressive aphasia (nfv-PPA) reflect a prominent neurodegenerative involvement of the frontal lobe networks, which may include the premotor and motor areas and thus cause heterogeneous clinical symptoms including parkinsonism. With the technique of transcranial magnetic stimulation, we investigated long-term potentiation- and long-term depression-like plasticity in the primary motor cortex of bv-FTD and nfv-PPA patients, with and without parkinsonism, by using the theta-burst stimulation (TBS) protocol. We applied the intermittent TBS and continuous TBS in 20 FTD patients and 18 age-matched healthy subjects. Results were also compared with those achieved in a cohort of age-matched patients with Parkinson's disease. The responses to TBS were abnormal in FTD patients with parkinsonism. By contrast, the TBS induced normal responses in patients with both nfv-PPA and bv-FTD without parkinsonism. Finally, responses to TBS were comparable in patients with FTD with parkinsonism and patients with Parkinson's disease. We provide evidence of abnormal primary motor cortex long-term potentiation-/long-term depression-like plasticity in patients with FTD and parkinsonism suggesting neurodegenerative processes in the corticobasal ganglia-thalamo-cortical motor networks in these patients.