Periodic limb movements in sleep and iron status in children

Abstract

Study Objectives: To assess potential relationships between serum iron and ferritin levels and the severity of periodic limb movement in sleep (PLMS) in a pediatric population, and to evaluate the response to supplemental iron therapy. Design: A prospective study of all consecutively diagnosed children with PLMS (periodic limb movement index [periodic limb movements per hour of total sleep time, [PLMI] >5) who underwent overnight polysomnographic evaluation. In all patients, complete blood count and serum iron and ferritin levels were obtained. Patients with serum ferritin concentrations less than 50 μg/L were prescribed iron sulfate at 3 mg/kg of elemental iron per day for 3 months. At the end of treatment, serum iron and ferritin levels and sleep studies were repeated. Setting: Comprehensive Sleep Medicine Center, Tulane University Health Sciences Center, and Kosair Children's Hospital Sleep Medicine and Apnea Center. Patients: Twenty boys and 19 girls with PLMS with a mean age of 7.5±3.1 years. Intervention: Iron therapy. Results: Twenty-eight (71.8%) patients had ferritin levels less than 50 μg/L. There was no significant correlation between serum ferritin concentration and PLMS severity as indicated by the PLMI (r=-0.19). The PLMI in patients with serum ferritin levels less than 50 μg/L (29.9±15.5 PLM/h) was higher than in patients with serum ferritin levels greater than 50 μg/L (21.9±11.8 PLM/h); however, the difference did not achieve statistical significance (P=0.09). In contrast, serum iron was significantly correlated with PLMI (r=-0.43, P<0.01). Indeed, patients with serum iron concentrations less than 50 μg/dL had a higher PLMI compared to patients with serum iron concentrations greater than 50 μg/dL (42.8±18.3 PLM/h and 23.1±10.1 PLM/h, respectively; P=0.02). Twenty-five out of the 28 PLMS patients with serum ferritin levels less than 50 μg/L received treatment with iron sulfate, and 19 (76%) responded favorably. Among the responders to iron therapy, PLMI decreased from 27.6±14.9 PLM per hour to 12.6 ± 5.3 PLM per hour after 3 months of iron supplements (P<0.001) and coincided with increases in serum ferritin levels (pre: 40.8±27.4 μg/L vs post: 74.1±13.0 μg/L; P<0.001). Conclusions: In children, the presence of PLMS is frequently associated with low serum iron and a tendency toward low serum ferritin levels. In addition, iron therapy is associated with clinical improvement in most of these patients.