Sleep-stage dynamics in patients with chronic fatigue syndrome with or without fibromyalgia

Abstract

Study objectives: Chronic fatigue syndrome (CFS) and fibromyalgia (FM) are medically unexplained conditions that often have overlapping symptoms, including sleep-related complaints. However, differences between the 2 conditions have been reported, and we hypothesized that dynamic aspects of sleep would be different in the 2 groups of patients.

Participants: Subjects were 26 healthy control subjects, 14 patients with CFS but without FM (CFS alone), and 12 patients with CFS and FM (CFS+FM)-all women.

Measurements and results: We studied transition probabilities and rates between sleep stages (waking, rapid eye movement [REM] sleep, stage 1 [S1], stage 2 [S2], and slow-wave sleep [SWS]) and duration distributions of each sleep stage. We found that the probability of transition from REM sleep to waking was significantly greater in subjects with CFS alone than in control subjects, which may be the specific sleep problem for people with CFS alone. Probabilities of (a) transitions from waking, REM sleep, and S1 to S2 and (b) those from SWS to waking and S1 were significantly greater in subjects with CFS+FM than in control subjects; in addition, rates of these transitions were also significantly increased in subjects with CFS+FM. Result (a) might indicate increased sleep pressure in subjects with CFS+FM whereas result (b) may be the specific sleep problem of subjects with CFS+FM. We also found that shorter durations of S2 sleep are specific to patients with CFS+FM, not to CFS alone.

Conclusions: These results suggest that CFS and FM may be different illnesses associated with different problems of sleep regulation.

Keywords: Sleep dynamics; chronic fatigue syndrome; duration distribution; fibromyalgia; transition probability; unrefreshing sleep.

Figure 1

Normalized transition probabilities between wake (W), rapid eye movement sleep (R), stage 1 sleep (S1), stage 2 sleep (S2), and slow-wave sleep (SWS) for healthy control subjects (white), those with chronic fatigue syndrome (CFS) alone (gray), and subjects with CFS+fibromyalgia (FM) (black). **P < 0.01 and *P < 0.05 by Mann-Whitney U test with Bonferroni corrections.

Figure 2

Transition rates per unit minute between wake (W), rapid eye movement sleep (R), stage 1 sleep (S1), stage 2 sleep (S2), and slow-wave sleep (SWS) for healthy control subjects (white), subjects with chronic fatigue syndrome (CFS) alone (gray), and subjects with CFS+fibromyalgia (FM) (black). **P < 0.01 and *P < 0.05 by Mann-Whitney U test with Bonferroni corrections.

Figure 3

Cumulative distributions for durations of sequential runs for wake and slow-wave sleep (SWS) in double logarithmic plots (A and D), and stage 1 sleep (S1), stage 2 sleep (S2), and rapid eye movement sleep (REM) in semilogarithmic plot (B, C, and E) for healthy control subjects (•), subjects with chronic fatigue syndrome (CFS) alone (Δ), and those with CFS+ fibromyalgia (FM) (×). Insets: Distributions for durations of sequential runs for wake and SWS in double logarithmic plot (A and D), S1 and REM sleep in semilogarithmic plot (B and C), and S2 in loglog-log plot (E) for healthy control subjects (•), those with CFS alone (Δ), and subjects with CFS+FM (×). Cumulative duration distributions for S2 sleep are presented not in loglog-log but in log-lin axis because cumulative distribution of stretched exponential function does not follow a straight line in loglog-log axis. **P < 0.01 and *P < 0.05 by Kolmogorov-Smirnov test with Bonferroni corrections.

Figure 4

Transition diagrams among waking (W), rapid eye movement sleep (R), stage 1 sleep (S1), stage 2 sleep (S2), and slow-wave sleep (SWS) stages showing significantly increased transition probabilities for subjects with chronic fatigue syndrome (CFS) alone and those with CFS+fibromyalgia (FM), compared with healthy control subjects (A); significantly decreased transition probabilities for subjects with CFS alone and those with CFS+FM, compared with healthy control subjects (B); and significantly different transition probabilities between subjects with CFS alone and those with CFS+FM (C). (A) Open arrow depicts significantly greater transition probability for subjects with CFS alone compared with healthy control subjects. Closed arrows depict significantly greater transition probability for subjects with CFS+FM compared with healthy control subjects. (B) Closed arrows depict significantly decreased transition probabilities for subjects with CFS+FM compared with healthy control subjects. Arrows with cross-hatching depict significantly decreased transition probabilities for both subjects with CFS alone and those with CFS+FM, compared with healthy control subjects. (C) Open arrow depicts significantly greater transition probability for subjects with CFS alone compared with subjects with CFS+FM. Closed arrows depict significantly greater transition probability for subjects with CFS+FM compared with those with CFS alone. In all 3 panels, arrow diameter is proportional to the transition probability for that particular transition. A circle, triangle, or square indicates that distributions follow a power-law, an exponential, and a stretched exponential function, respectively.