Stimulation over the cerebellum with a regular figure-of-eight coil induces reduced motor cortex inhibition in patients with progressive supranuclear palsy

OBJECTIVE: To determine whether motor cortex inhibition by stimulation over the cerebellum with a figure-of eight coil (MISC8) may be reduced in patients with Progressive Supranuclear Palsy (PSP).
METHODS: Paired pulse TMS was used to evaluate MISC8, in patients with different forms of parkinsonism and dementia. The primary outcome measures were sensitivity and specificity of motor cortex inhibition, derived from receiver operator curve analysis, in discriminating PSP from other neurodegenerative disorders.
RESULTS: A total of 150 participants met inclusion criteria. According to clinical criteria, the study population included 19 PSP, 26 Parkinson's disease, 25 dementia with Lewy bodies, 15 corticobasal syndrome, 25 frontotemporal dementia and 15 Alzheimer's disease patients, and 25 healthy controls. PSP patients were characterized by a specific impairment of MISC8 (0.99 ± 0.08) compared to the healthy control group and to other neurodegenerative disorders (mean range = 0.63-0.80, all p-values<0.001). Using the best cut-off index, MISC8 differentiated PSP from other diagnoses with an overall sensitivity of 100%, a specificity of 94%, and an accuracy of 97%.
CONCLUSIONS: TMS is a non-invasive procedure which reliably distinguishes PSP from other neurodegenerative disorders. MISC8 could represent a useful additional diagnostic tool to be used in clinical practice.