Asymmetry of Permutation Entropy in Early Creutzfeldt-Jakob Disease: A Clue to a Specific Pathological Process?

Objective: We used permutation entropy (PE) to disclose abnormalities of cerebral activity in patients with early genetic or sporadic Creutzfeldt-Jakob disease (CJD), as compared to patients with steroid-sensitive subacute encephalopathies (SSE) and healthy volunteers (HV). Methods: We evaluated 16 EEG of CJD patients, 21 of SSE patients and 33 of HV. EEG of CJD patients were performed at an early stage and didn’t show periodic sharp wave complexes. Diagnosis of SSE was established on clinical and laboratory data. PE was estimated channel by channel. Average PE of all channels and the mean PE values of channels belonging to right and left hemispheres were calculated. The following variables were analysed: age at inclusion, sex, total average PE and mean interhemispheric PE differences. Results: Average PE was significantly lower in CJD patients as compared to HV (mean 0.72, SD 0.03 vs. mean 0.75, SD 0.02, p=0.01). Mean interhemispheric PE difference was higher (mean 0.009, SD 0.006) in CJD patients as compared to both SSE (mean 0.005, SD 0.003) and HV groups (mean 0.004, SD 0.004) (p=0.02). Discussion: The lower average PE value in CJD compared to HV group demonstrates a reduction of EEG complexity that suggests disruption of thalamo-cortical connection since the early phases of disease. Moreover, subjects with CJD showed a significant interhemispheric asymmetry in PE values, indicating that the pathological process of CJD may be initially asymmetric. This study confirms that PE may represent a useful tool to reveal abnormalities of cerebral electric activity not revealed by conventional EEG recordings.