Periodic limb movement disorder, previously known as nocturnal myoclonus, is defined as involuntary movements of the patient’s limb or torso during awake or sleep which the patient is not aware of, different from the voluntary movement of the limb to relieve the discomfort in RLS patients (Hening et al., 1999; Trenkwalder et al., 2005). Nevertheless, it’s a very common phenomenon in RLS patients. A previous study indicated that PLMS was found in around 80% of RLS patients (Montplaisir et al., 1997). On the contrary, not a large percentage of patients having PLMS presented RLS. PLMS, which is not a specific feature for RLS patients, can be associated to many other conditions. The PSG is usually employed to measure the movements, while actigraphy is a helpful method for diagnosing and measuring PLMW or PLMS. PLMS is diagnosed on PSG by at least continuous four muscle contractions lasting 0.5–10 s and recurring during intervals of 5–90 s. The minimum amplitude of a leg movement event is an 8 μV increases in EMG voltage above resting EMG (Iber et al., 2007) in diagnostic criteria for PLMD.