May 7, 2001 (Philadelphia) -- Adults with restless leg syndrome, who can't keep still even when they're asleep, are more likely than others to have attention deficit hyperactivity disorder (ADHD), report researchers here at the annual meeting of the American Academy of Neurology.
People with restless leg syndrome, or RLS, report feeling discomfort in their legs when they are sleeping or inactive. The sensations range from a mild tingling to a feeling of creeping, crawling, pulling, or pain. One or both legs may be affected, with the sensations occurring when the person is sitting still -- in the office, at the movies, etc. -- or lying down.
"Some patients are so bad that the minute they sit down or lie down, the symptoms begin again and they have to start anew by getting out of bed and walking or pacing," says Arthur Walker, MD, a neurologist with the New Jersey Neuroscience Institute at JFK Medical Center in Edison and professor of neuroscience at Seton Hall University in South Orange, N.J.
"Nighttime is the worst time for these patients -- they're lying down to go to sleep, and they can't," he says. As many as 10% of adults may have RLS, with symptoms ranging from mild to severe, he says.
In a study looking at 56 adults with RLS and 77 adults without the condition, nearly 40% of those with restless legs were deemed to have "probable" ADHD, compared with only 14% of people without RLS. When it came to having "highly probable" ADHD, 21% of those with RLS qualified, compared with only 4% of the other subjects.
The study suggests that, "people with RLS should also be tested for ADHD and vice versa. That way, these disorders can be diagnosed and treated more effectively," says Mary L. Wagner, PharmD, at Rutgers University in Piscataway, N.J.
According to the National Institutes of Health, ADHD is the most commonly diagnosed behavioral disorder of childhood, affecting an estimated 3-5% of school-age children. Kids with ADHD have a hard time concentrating or paying attention in school and at home, are easily distracted, and behave impulsively. ADHD can also have long-term effects on academic performance, career success, and relationships.
Because children with ADHD often have RLS and a related problem called periodic limb movements of sleep, the researchers questioned whether adults with RLS might also have ADHD that had gone unrecognized.
"The leg discomfort from RLS could cause people to be more hyperactive and distractible, and being tired could cause people to be more inattentive," Wagner says.
"We often miss the diagnosis in children since the symptoms are so benign, or parents think they are related to growing pains, or the children don't know what it means," says Wagner.
Wagner and colleagues speculate that RLS and ADHD could be genetically linked, which might explain why they appear together frequently, or that the leg discomfort from RLS and associated sleep disruption could cause ADHD-like symptoms.
Another theory holds that both ADHD and RLS may be caused by a shortage in the brain of dopamine, a chemical messenger that is partly responsible for the control of movement; lack of dopamine-producing nerve cells in the brain is a major hallmark of Parkinson's disease.
In studies of children with ADHD who do not respond well to the standard therapy with Ritalin and are treated instead with drugs that enhance dopamine production and transport in the brain, Walker and colleagues found that the therapy also appeared to improve symptoms of RLS.
The researchers say that adults with ADHD and RLS may have improvement of symptoms with drugs that enhance dopamine use in the brain. Although in patients with Parkinson's disease such drugs can cause jerky or uncontrolled movements, their primary side effect in people with ADHD tend to be nausea, vomiting, lightheadedness, or fainting.
"People from the Massachusetts General Hospital at Harvard University have estimated that only about 30% of the people have ADHD by itself," says Michael E. Finkel, MD, a neurologist at the Cleveland Clinic in Naples, Fla., who commented on the RLS/ADHD study for WebMD.
"Those who have the ADHD 'complex' have other disorders which can be recognized and treated," he says, so the more a doctor knows about a patient's medical history, the better positioned he is to treat that patient.