Intravenous low molecular weight iron dextran appears to provide effective long-lasting treatment for some patients with restless leg syndrome (RLS), even for those with normal serum ferritin levels, research indicates.
The results showed that 68% of 25 patients with RLS showed moderate or complete improvement of all RLS symptoms after treatment according to a Korean-translated version of the International RLS Severity (K-IRLS) scale and the PAM-RL device, which records periodic leg movements.
However, as reported in Sleep Medicine, the researchers saw no correlation between increases in cerebrospinal fluid (CSF) ferritin in response to therapy and clinical improvements.
"Although a relatively accessible measure, CSF ferritin is at best a crude measure of CNS [central nervous system] iron status and not necessarily reflective of regionally specific changes in iron status that are assumed to account for the symptom development," say Yong Won Cho, from Keimyung University School of Medicine in Daegu, South Korea, and colleagues.
"In addition, the narrow range of symptom severity in this study may have limited our ability to find any differences between CSF ferritin and subjective measures of the disease."
The RLS patients were given four iron dextran 250 mg infusions. Before treatment, the average K-IRLS score was 23.5 and the average PAM-RL index was 30.6. Fourteen of the patients had a serum ferritin level below 50 ng/mL.
Three weeks after treatment, the average K-IRLS score had fallen significantly to 16.7 and the average PAM-RL index dropped significantly to 11.2.
Symptom improvement started between 1 and 6 weeks after treatment and treatment benefits lasted from 2 to 97 weeks. Only eight (32%) patients showed no improvement.
In an analysis of 23 patients, levels of both serum ferritin and CSF ferritin had increased significantly at 3 weeks post-treatment, from an average of 41.0 ng/mL before treatment to 274.4 ng/mL, and from 7.2 ng/mL to 8.8 ng/mL, respectively.
Changes in K-IRLS scores did not correlate with changes in CSF ferritin level, however, and neither pre-treatment serum or CSF ferritin nor patient demographics were predictive of treatment response.
"An important focus of future research, therefore, should be finding clinical, biological, or genetic markers that would help predict those who will respond to IV [intravenous] iron treatment," the researchers conclude.
"Until that occurs, however, the question is open as to whether or not we should be treating all RLS with IV iron with doses to increase ferritin in the high normal range.
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