Prominent Prolongation of Cortical Silent Period Induced by Transcranial Magnetic Stimulation in Creutzfeldt-Jakob Disease

The cortical silent period (CSP) induced by transcranial magnetic stimulation (TMS) has been reported to be prolonged in 2 Creutzfeldt-Jakob disease (CJD) patients who presented with periodic myoclonus. Herein, we will show a prominent prolongation of TMS-induced CSP in a patient with CJD who did not have periodic myoclonus. The patient was a 66-year-old woman who developed rapidly progressive dementia. No myoclonic jerks were observed. Brain magnetic resonance imaging showed high-intensity lesions in the cerebral cortex, basal ganglia, and thalamus on diffusion-weighted images. Electroencephalography (EEG) showed diffuse and continuous slow waves, but no periodic synchronous discharges (PSDs). A TMS study revealed that the duration of CSP was prominently prolonged: the duration of CSP (370 ms) equaled that of the mean + 6.5 SD of the normal value. One month after admission, the patient exhibited akinetic mutism and developed periodic myoclonus in her limbs. The clinical course was compatible with CJD. To date, CSP has been measured in only 2 CJD patients. The common findings in both cases were marked prolongation of CSP, periodic myoclonus, and PSD on EEG. In short, we demonstrated that TMS-induced CSP was prominently prolonged even at the early stage of CJD without periodic myoclonus or PSD. In other disorders, the CSP has not been reported to be comparably prolonged to that of CJD patients. Therefore, we conclude that TMS-induced CSP could be prominently prolonged even in the early stage of CJD. The marked prolongation of the CSP might be an early biomarker of CJD.