JHU researchers find possible link between brain chemical, RLS

Johns Hopkins researchers believe they may have discovered an explanation for the sleepless nights associated with restless leg syndrome, a symptom that persists even when the disruptive, overwhelming nocturnal urge to move the legs is treated successfully with medication.

Neurologists have long believed RLS is related to a dysfunction in the way the brain uses the neurotransmitter dopamine, a chemical used by brain cells to communicate and produce smooth, purposeful muscle activity and movement. Disruption of these neurochemical signals, characteristic of Parkinson's disease, frequently results in involuntary movements. Drugs that increase dopamine levels are mainstay treatments for RLS, but studies have shown they don't significantly improve sleep. An estimated 5 percent of the U.S. population has RLS.

The small new study, headed by Richard P. Allen, an associate professor of neurology at the Johns Hopkins University School of Medicine, used MRI to image the brain. Researchers found glutamate, a neurotransmitter involved in arousal, in abnormally high levels in people with RLS. The more glutamate the researchers found in the brains of those with RLS, the worse their sleep.

The findings are published in the journal Neurology.

"We may have solved the mystery of why getting rid of patients' urge to move their legs doesn't improve their sleep," Allen says. "We may have been looking at the wrong thing all along, or we may find that both dopamine and glutamate pathways play a role in RLS."

For the study, Allen and his colleagues examined MRI images and recorded glutamate activity in the thalamus, the part of the brain involved with the regulation of consciousness, sleep and alertness. They looked at images of 28 people with RLS and 20 people without. The RLS patients included in the study had symptoms six to seven nights a week persisting for at least six months, with an average of 20 involuntary movements a night or more.

The researchers then conducted two-day sleep studies in the same individuals to measure how much rest each person was getting. In those with RLS, they found that the higher the glutamate level in the thalamus, the less sleep the subject got. They found no such association in the control group without RLS.