Sleep microstructure in patients with systemic sclerosis: A cyclic alternating pattern analysis study

The cyclic alternating pattern (CAP) is a cyclic variation of sleep electroencephalogram activity within non-rapid eye movement (non-REM) sleep and increased CAP is the marker of sleep instability. The present study aimed to examine the expression of cyclic alternating pattern in non-REM sleep in patients with systemic sclerosis (SSc) and to compare these findings with the control group. Thirty-one patients with SSc were compared with matched controls by age, gender, body mass index, and apnea-hypopnea index (AHI). Sleep measurements were obtained by standard polysomnography with conventional sleep scoring. A CAP analysis was performed and verified by certified somnologists. The sleep parameters of the SSc and control groups were similar for sleep efficiency, sleep stage percents N1, N2, N3, sleep latency, and minimum oxygen saturation (p = 0.627, p = 0.693, p = 0.530, p = 0.736, p = 0.772, and p = 0.693, respectively). The SSc patients presented a higher arousal and periodic limb movement index. The CAP analyses showed that SSc patients had higher CAP numbers, phase A2 index, A3 duration, and lower A1 duration (p = 0.032, p = 0.016, p = 0.016, and p = 0.016, respectively). Overall the phase A2 index, A2 total time during non-REM sleep were significantly higher and the A1 duration was significantly lower in SSc patients, although sleep efficiency and the distribution of sleep macro-structure seem to be similar to the control group. This study emphasises that microstructure analysis performed with CAP provides information that would otherwise be lost if only macrostructure analysis were considered.