Restless Sleep Disorder and the Role of Iron in Other Sleep-Related Movement Disorders and ADHD

In the last few years, restless sleep has been described as the key element of many clinical issues in childhood, leading to the recognition of "restless sleep disorder" (RSD) as a new proposed diagnostic category. The essential aid of video-polysomnographic recordings enables detection and quantification of the "large muscle group movements" (such as limb movements and repositioning) frequently described by parents of children with RSD. Strong evidence links iron deficiency to the pathophysiology of sleep-related movement disorders such as RSD, restless legs syndrome, periodic limb movement disorder, and attention deficit hyperactivity disorder (ADHD) due to the important role played by the brain dopamine production system. Serum ferritin is the main parameter used to evaluate iron deficiency in patients with sleep-related movement disorders. Iron supplementation is recommended when the serum ferritin level is <50 ng/mL, since the literature emphasizes the correlation between lower levels of serum ferritin, serum iron, and cerebrospinal fluid ferritin, and increased symptom severity. Moreover, several studies report an improvement in symptoms when ferritin levels are kept above 50 ng/mL. In this narrative review, we discuss the role of iron in sleep-related movement disorders, as well as ADHD, highlighting not only the connection between these two conditions, but also the relevance of iron supplementation for symptom improvement.