Negative myoclonus in Creutzfeldt–Jakob disease

Objective: To describe electrophysiological findings in a patient with Creutzfeldt–Jakob disease (CJD) showing negative myoclonus. Methods and results: We studied this CJD patient electrophysiologically, in comparison with two patients with cortical reflex positive myoclonus due to benign adult familial myoclonic epilepsy (BAFME). Spontaneous negative myoclonus was associated with periodic synchronous discharges (PSDs) on the electroencephalogram, but negative myoclonus could also be induced by electrical stimulation of the median nerve in the CJD patient. This patient showed giant somatosensory evoked potentials (SEPs) and enhanced C reflexes, and the duration of the induced EMG silences was found to be significantly correlated with the amplitude of cortical SEPs. The duration of silent periods (SPs) produced by magnetic stimulation of the motor cortex was extremely long. The study of recovery function of SEPs suggested that the excitability of the somatosensory cortex was decreased during a long post-stimulus period. These findings were clearly different from those of patients with BAFME. Conclusions: This CJD patient had two types of negative myoclonus; one was associated with PSDs and the other was cortical reflex negative myoclonus. The long-lasting decrease in excitability of the sensorimotor cortices after stimulation could be related to the occurrence of both types of negative myoclonus.