Correlation between systemic iron parameters and substantia nigra iron stores in restless legs syndrome

To evaluate the relation between systemic iron parameters (SIP) and substantia nigra (SN) iron deposits, as assessed by transcranial sonography (TCS) in restless legs syndrome (RLS). We conducted a cross-sectional study in RLS patients, from whom blood samples with SIP were obtained, consisting of total iron-binding capacity (TIBC), serum ferritin, hemoglobin, transferrin saturation (TSAT), serum iron, and serum transferrin. TCS was performed over the SN, and the substantia nigra echogenicity index (SNEI) was determined according to established methods. Symptom severity was evaluated using the international restless legs scale (IRLS). A Spearman correlation was performed. A total of 167 patients were studied. Correlations between SNEI and SIP were as follows: serum ferritin (R = 0.0422; n.s.), TSAT (R = 0.0883; n.s.), TIBC (R = −0.1091; n.s.), serum transferrin (R = −0.0420; n.s.), hemoglobin (R = 0.0185; n.s.), serum iron (R = 0.0389; n.s.). No correlation was found with age and IRLS (R = 0.1375; n.s. and R = 0.0880, n.s., respectively). SIP are not correlated with SN iron content in RLS, quantified by means of TCS. TCS of the SN might be a more valid estimate and could be useful in the evaluation of RLS patients. •Substantia nigra iron stores are not correlated with systemic iron parameters in RLS.•Substantia nigra iron deposits in RLS cannot be predicted by any systemic iron parameter.•Transcranial sonography enables the direct quantification of substantia nigra iron deposits.