Circadian rhythm of restless legs syndrome: relationship with biological markers

Recently, it was suggested that the intensity of restless legs syndrome (RLS) symptoms may be modulated by a circadian factor. The objective of this study was to evaluate, during a 28-hour modified constant routine, the nycthemeral or circadian variations in subjective leg discomfort and periodic leg movements (PLMs) and to parallel these changes with those of subjective vigilance, core body temperature, and salivary melatonin. Seven patients with primary RLS and seven healthy subjects matched for sex and age entered this study. Although the symptoms were more severe in patients than in controls, a significant circadian variation in leg discomfort and PLM (p < 0.01) was found for both groups. In both groups, the profiles of leg discomfort and PLM were significantly correlated with those of subjective vigilance, core body temperature, and salivary melatonin. However, among these variables, the changes in melatonin secretion were the only ones that preceded the increase in sensory and motor symptoms in RLS patients. This result and those of others studies showing that melatonin exerts an inhibitory effect on central dopamine secretion suggest that melatonin might be implicated in the worsening of RLS symptoms in the evening and during the night.