Study objectives: It is now well established that symptoms of restless legs syndrome (RLS) are worsened by immobility and that their severity fluctuates according to a circadian pattern with a maximum occurring in the late evening or during the night. However, no study has ever attempted to dissociate these two effects. The objective of this study was to evaluate the nycthemeral variations in the effects of duration of immobility on symptoms of RLS.
Design: A 28-hour modified constant routine protocol.
Setting: Sleep Disorders Center, Montreal Sacré-Coeur Hospital.
Participants: Seven patients with primary RLS (3 men, 4 women; mean age: 43.9 years) and seven controls matched for age (42.4 years) and gender.
Intervention: None.
Measurements and results: A 40-minute Suggested Immobilization Test (SIT) was repeated every 2 hours during the 28-hour protocol in order to quantify both subjective leg discomfort and periodic leg movements (PLM). Regarding leg discomfort, a two-way ANOVA performed on patients' data revealed a significant interaction (p = 0.037) between Time within the SIT and Time of day. Simple effect analyses performed to decompose the interaction showed that the increase in leg discomfort with duration of immobility was found only on SIT 7, 8, 9, 10 and 12, which corresponds to the period between 21:20 and 08:00. In addition, in patients, a significant circadian variation (p < 0.01) was found for the 28-hour profiles of leg discomfort progression during the SIT. No interaction or Time within the SIT effect was found for controls.
Conclusions: These results show that worsening of RLS symptoms by immobility is closely linked to their intrinsic circadian variation.