There is no consensus about mechanisms underlying restless legs syndrome (RLS), 
also known as Willis-Ekbom disease (WED). Cortical excitability may be abnormal 
in RLS. Transcranial magnetic stimulation (TMS) can provide insight about 
cortical excitability. We reviewed studies about measures of excitability to TMS 
in RLS. Original studies published between January 1999 and January 2015 were 
searched in PubMed, Scopus, and Web of Science databases. Inclusion criteria 
were as follows: original studies involving primary RLS in patients from both 
sexes and ages between 18 and 85 years; TMS protocols clearly described; and 
they were written in English, in peer-reviewed journals. Fifteen manuscripts 
were identified. TMS protocols were heterogeneous across studies. Resting motor 
threshold, active motor threshold, and amplitudes of motor-evoked potentials 
were typically reported to be normal in RLS. A reduction in short-interval 
intracortical inhibition (SICI) was the most consistent finding, whereas 
conflicting results were described in regard to short-interval intracortical 
facilitation and the contralateral silent period. Decreased SICI can be reversed 
by treatment with dopaminergic agonists. Plasticity in the motor cortex and 
sensorimotor integration may be disrupted. TMS may become a useful biomarker of 
responsiveness to drug treatment in RLS. The field can benefit from increases in 
homogeneity and sizes of samples, as well as from decrease in methodological 
variability across studies.