Circadian pattern in restless legs syndrome.

This chapter provides an overview of circadian pattern in restless legs syndrome (RLS). Circadian variation of symptoms is a known feature of RLS. According to one of the five essential criteria for RLS diagnosis, symptoms "only occur or are worse in the evening or at night than during the day." RLS symptoms are most pronounced in the evening and at night, with a relative improvement in the late sleep period or in the early morning. This unique feature helps differentiating RLS from other movement disorders. Although differentiating the circadian pattern of RLS manifestations from the worsening of RLS symptoms at rest is not always easy, the independency of these two features has been demonstrated in several studies. Mechanisms implicated in circadian variations of RLS include dopamine, iron, opioids, and genetic factors, which all interact with each other. Further insights on circadian fluctuations in patients with RLS derive from clinical studies reporting circadian variations in sensory processing and spinal excitability, as well as from studies showing circadian variations in cortical excitability, default mode network, and cognition in patients with RLS.