A new Mayo Clinic study has for the first time established rates of restless legs syndrome in children, finding that almost 6 percent of children seen in Mayo's sleep clinic have the disease. The study, published in this month's issue of Annals of Neurology, also notes that the most common risk factors for the disease in kids are family history of restless legs syndrome and iron deficiency.
"Restless legs syndrome is underdiagnosed in kids," says Suresh Kotagal, M.D., chair of Mayo Clinic pediatric neurology and a sleep specialist. "If you look at children with difficulty falling asleep, you'll see a fair number have restless legs. Thus far, there have been sporadic case reports, but nobody has studied a larger group of children, looking at children with insomnia complaints as a whole to see how many had restless legs syndrome."
Dr. Kotagal and his colleague Michael Silber, M.B.Ch.B., Mayo Clinic neurologist and sleep specialist, indicate that restless legs syndrome may account for some of the age-old notion of "growing pains."
"It's been known for decades that children have 'growing pains,'" says Dr. Kotagal. "Studies by other investigators have now shown that growing pains in some children may actually be restless legs syndrome."
Dr. Kotagal says that while infrequent "growing pains" may be immaterial, parents and children should be alert for a habitual pattern of discomfort in the limbs around bedtime.
"Occasional growing pains are nothing to worry about, but growing pains every night may be restless legs syndrome," he says. "It's like the fact that somebody might snore one or two days a month, but if it happens every night, it may be something that needs medical attention."
The study examined the records of 538 children who had been seen in the pediatric sleep disorders program at Mayo Clinic between Jan. 2000 and March 2004. New, rigidly defined diagnostic criteria established by a consensus conference of the National Institutes of Health and the International Restless Legs Syndrome Foundation in 2003 allowed the Mayo Clinic researchers to classify their 32 patients as having probable restless legs in nine cases and definite restless legs syndrome in 23 cases. Those in the probable restless legs syndrome group were more likely to be younger. The most common symptoms were trouble getting to sleep or staying asleep, which affected 87.5 percent. One commonality in the restless legs syndrome patients was a low iron level in the blood (as measured by serum ferritin) seen in 83 percent of the patients, the explanation for which is unknown, according to Dr. Kotagal.
"With regard to the iron deficiency, we don't know if it's the diet or a genetic predisposition to low iron levels," says Dr. Kotagal. Drs. Kotagal and Silber also found family history of restless legs syndrome in 23 out of 32 patients identified to have restless legs syndrome in the study, or 72 percent. The child's mother was three times more likely to be the parent affected with restless legs syndrome.
"There seems to be a strong genetic component in restless legs syndrome," says Dr. Kotagal. "Very often when taking the medical history with the child, the parents say they have a similar condition."
An additional characteristic seen in 25 percent of the patients was inattentiveness.