Restless legs syndrome and Parkinson's disease

We were highly surprised on reading the recent article by Peralta et al., in which an augmented prevalence of restless legs syndrome (RLS) in patients with Parkinson's disease (PD) has been reported, without mentioning at all (and consequently having excluded) the well-established conditions causing secondary forms of the sensory-motor disorder, possibly occurring in the patients studied, and without including their own control population. This could have biased the results producing an overestimate of the frequency of assumed "primary" RLS in their patients, consequently corroborating the currently controversial issue of a significant comorbid association between the two disorders. Indeed, in our recently published survey on 118 PD outpatients the exclusion of secondary causes of RLS, and therefore, only considering the assumed "primary" forms of the disorder, resulted in a further reduced statistically not significant frequency of RLS in PD patients. In addition, in our study, only a limited proportion of PD patients, that is, 30 of 118 (25.4%), presented with motor fluctuations such as levodopa (L-dopa) end-of-dose deterioration, and among them only one patient, that is, 3.3%, was found suffering from assumed "primary" RLS. In contrast, the finding that in the study by Peralta et al. the majority of PD patients with RLS-like symptoms, that is 20 of 28 (71.4%), were presenting with Ldopa-related motor fluctuations or, conversely, that 28 of 75 patients, (37.3%) with motor fluctuations scored positive for RLS indicates that the occurrence of confounding conditions, that is, "mimics" of RLS, were particularly relevant in their population of PD patients. Therefore, the conclusion of the authors that their study "suggests that RLS-like symptoms are part of the sensory-motor spectrum of wearing-off in Ldopa treated PD" only confirms the well-known notion that "mimics" of RLS may confound the detection of "true" RLS in these patients, making, in our opinion, the results of their study, as well as those of some others in which the presence of motor fluctuations has not been quoted poorly reliable in supporting the comorbid association of PD and assumed "primary" RLS. Because of these considerations, it would have been preferable to have titled the paper by Peralta et al. "Restless Legs-like Syndrome in Parkinson's Disease.