Sleep microstructure in Parkinson's disease: cycling alternating pattern (CAP) as a sensitive marker of early NREM sleep instability.

BACKGROUND: Sleep disorders are frequent in Parkinson's disease (PD). Apart from the occurrence of REM behavior disorders, in the early phase of the disease standard sleep macrostructure evaluation was inconclusive. OBJECTIVE: We analyzed non-rapid eye movement (NREM) sleep microstructure (CAP) in a group of PD patients to provide an objective measure of sleep disruption. METHODS: We recruited 31 PD patients [mean age 59.5 ± 12.4 years; mean Hoehn-Yahr (H-Y) stage: 3.4 ± 1.8] and 34 age-matched non-parkinsonian subjects (mean age 61.5 ± 15.2 years) as a control group. All patients underwent full-night laboratory polysomnography (PSG). Conventional sleep macro/microstructure analysis was performed. Patients were then divided into two groups: group 1 (H-Y stage ≤ 2) and group 2 (H-Y stage ≥ 3). RESULTS: In group 2 PD patients compared to controls, alterations of both sleep macrostructure and microstructure were found. The PD subgroup with milder disease (group 1) presented sleep macrostructure, movements and respiratory parameters not significantly different from controls, although their CAP rate was significantly higher and the proportion of the A1 phase of CAP was reduced (p = 0.03). Multivariate logistic regression showed that disease duration, disease severity, and arousal index emerged as independent predictive factors for CAP rate ≥55% and the A1 phase of CAP ≤40% (p < 0.05). CONCLUSION: The main result of our study consists in the disclosure of altered NREM sleep microstructure in PD even at an early stage of the disease, suggesting an early alteration of the central pathways involved in the NREM sleep building-up and stability.