Clinical Factors Related to the Response of IV Ferric Carboxymaltose Treatment in Patients with Restless Legs Syndrome

ABSTRACT

OBJECTIVES: Significant benefit of intravenous ferric carboxymaltose (FCM) for restless legs syndrome (RLS) has been demonstrated. However, clinical indicators to expect treatment response of RLS are not clarified. The aim of this study is to find out determinant factors to predict treatment outcome of FCM. METHODS: We enrolled consecutive 108 patients with RLS who visited sleep clinic and received FCM from April 2016 to November 2017. Obtained data were detailed history including international restless legs scale (IRLS) and questionnaires, comorbid diseases, medication. Complete blood cell count, serum iron, ferritin, and total iron-binding capacity were sampled before and after treatment. Treatment response was assessed about four weeks after FCM administration. Patients with more than 40% decrease on IRLS were classified into the responders. RESULTS: 99 patients (mean 54.5 y and 79 females) were included. 58 patients (58.6%) were classified to be responders. There were substantial differences in post-treatment IRLS and symptom reduction rate between responders (7.4±6.4, 77.5±18.6%) and non-responders (29.7±8.7, 7.4±10.3%). No significant differences were found in demographics, baseline IRLS, sleep, and mood status between two groups. Serum ferritin and transferrin saturation was significantly lower in responders (37.6 ng/mL, 25.0%) than non-responders (55.1 ng/mL, p=0.014 and 36.5%, p=0.001). Patients with a history of gastrectomy (n=8) showed an excellent response to FCM (83.8% of symptom reduction). Comorbid lumbosacral radiculopathy had lower response rate (29.4%). CONCLUSIONS: Peripheral iron compromised state and gastrectomy history may indicate good response to intravenous FCM in patients with RLS. Patients with lumbosacral radiculopathy tend to be poor responders to intravenous FCM.