Barnes T, Rosen GM. Understanding the questions parents are asking. J Clin Sleep Med. 2019;15(11):1701.
Restless sleep and daytime neurobehavioral symptoms such as fatigue, irritability, and impulsivity are frequently seen in the same child. The parents of these children have observed their child’s restless sleep, but their primary concern is often their child’s daytime neurobehavioral symptoms. Thus, they bring their children to a pediatric sleep center for an evaluation with the question, “are the daytime symptoms caused by a sleep disorder and will improving the night time sleep result in an improvement in the daytime symptoms?” When these children present to a sleep center, a serum ferritin level is routinely checked and is often < 50 ng/mL (the median ferritin level in US children is 30). A subset of these children meet diagnostic criteria for restless legs syndrome (RLS), and others meet criteria for the proposed diagnosis of restless sleep disorder. Drs. Ingram and Al-Shawwa1 have seen these children in Kansas City, Dr. DelRosso2 has seen these children in San Francisco, and we have seen them in Minnesota. The parents have observed there is a relationship between restless sleep and daytime behavioral symptoms and they want the sleep clinician to help them understand the nature of that relationship. That is, is the relationship between the child’s sleep and daytime neurobehavioral symptoms causal or coincidental? If sleep disruption is the cause of the daytime symptoms then the best intervention is obviously to address the sleep problem; if the sleep disruption is merely coincidental, then improvement in sleep may have little impact on the daytime symptoms. We have complicated this question for the parents and extended the chain of causality, by evaluating the child’s iron status.
Our study looked for a relationship between RLS symptom severity and serum ferritin level and found that the relationship was modest at best. Though some children’s sleep improved significantly with iron treatment, for most, the benefits were not dramatic. If this observation is confirmed in future studies it should impact both how sleep clinicians treat restless legs and restless sleep in children and the larger question of how we answer parents who ask, “are my child’s daytime symptoms the result of a sleep disorder?”
The reason for the lack of correlation between serum ferritin and RLS symptom severity is not understood fully. Restless legs is a complex, multifactorial clinical problem, and low serum ferritin level is just one, and likely not the most important, of the determinants of symptom severity.
As Drs. Ingram and Al-Shawwa advised, parents should not be alarmed by a diagnosis of low serum ferritin or mild iron deficiency, though especially in growing children, use of supplemental iron to bring the serum ferritin level to > 50 ng/mL is recommended.
The authors report no conflicts of interest.