Analysis of slow and fast sleep spindle properties in Parkinson's disease - A comparative EEG study

Sleep disturbances and altered sleep macrostructure are common in Parkinson's disease (PD). Few studies have addressed the changes in sleep spindle (SS) properties in this movement disorder so far. SS seem to be fundamental of both sleep architecture and memory consolidation. The aim of our comparative study was to investigate the changes of SS characteristics in PD, and reveal the relationship between SS properties and cognitive function.

We investigated 20 PD patients and 18 age-matched controls. All participants underwent a 24-hour-long polygraphic EEG recording after extensive clinical investigation. We detected slow and fast SS properties automatically using individual adjusting method (IAM). The data were statistically evaluated.

We found significantly lower fast spindle amplitude in PD comparing with controls. We did not find significant differences in SS densities, duration and oscillatory frequency between the groups. We detected significant positive correlation between fast SS amplitude and memory in PD, and between fast SS density and retrograde memory in controls. The total Addenbrooke's cognitive score correlated negatively with slow SS density and duration in controls.

By the time clinical diagnosis of PD is established, the pathological process is already spreading. Changes in sleep macrostructure and SS properties might become a useful biomarker of the neurodegenerative process in PD. In addition, decreased fast SS amplitude might predict further cognitive deterioration and indicate early involvement of corresponding cortical area. Our study results strengthen the importance of EEG examination in PD, and the use of IAM method in SS analysis.