Decreased serum ferritin may be associated with increased restless legs syndrome in Parkinson's disease (PD): a meta-analysis for the diagnosis of RLS in PD patients

Objective: Restless legs syndrome (RLS) is one of the most common non-motor symptoms of Parkinson's disease (PD), but its pathogenesis in a PD background is unclear. Abnormal iron metabolism may be involved, in which case it may be a marker of RLS risk. Here, the literature was systematically searched and meta-analyzed to compare iron metabolism markers between PD patients with or without RLS. Method: The databases PubMed, Embase, Chinese National Knowledge Infrastructure, Wanfang, Web of Science, and SinoMed were searched for case-control and observational studies examining RLS-related changes in iron metabolism in PD, in terms of serum iron, serum ferritin and hemoglobin. Eligible studies were meta-analyzed using Stata 12.0. Results: Meta-analysis of 11 case-control studies showed that serum ferritin concentration was lower in PD patients with RLS than in those without RLS. (95%CI -0.32 to -0.03, p = 0.018). In contrast, levels of serum iron or hemoglobin did not differ significantly between PD patients with or without RLS. Conclusion: This meta-analysis may provide the first reliable pooled estimate of the correlation between abnormal iron metabolism and RLS in PD. The available evidence indicates that levels of ferritin, but not of serum iron or hemoglobin, correlate significantly with RLS in PD, with lower ferritin levels correlating to greater prevalence of RLS.