Urinary 6-hydroxy-melatonin-sulfate excretion and circadian rhythm in patients with restless legs syndrome.

The precise etiology of the restless legs syndrome (RLS) is unknown. Sensory and motor symptoms of RLS worsen during evening/night, coincident with the physiological peak of pineal melatonin excretion. Decreased melatonin levels have been reported in insomnia, which is an associated feature of RLS. Melatonin substitution improved insomnia. A potential association between the idiopathic RLS (iRLS) and alterations in melatonin excretion was therefore explored. Daytime (7:00-22:00 hr) and night-time (22:00-7:00 hr) urinary excretion of 6-OH-melatonin-sulfate (aMLTs) was measured in 15 patients with iRLS and 11 controls by a radioimmunoassay. There was no significant difference between daytime and night-time urinary aMLTs excretion in iRLS as compared with controls (daytime: 6.14 +/- 5.20 ng versus 5.02 +/- 5.11 ng, NS; night-time: 21.07 +/- 17.05 ng versus 22.92 +/- 16.52 ng, NS). Our data do not provide evidence for a decrease of cumulative melatonin production in iRLS. Insomnia in RLS does not seem to be correlated with a deficit of melatonin.