Both Attention Deficit Hyperactivity Disorder (ADHD) & Restless Leg Syndrome (RLS) individuals have a common problem – Dopamine deficiency. The difference lies at the major site of dopamine action. Both ADHD and RLS can cause disruptive problems with a need to move, but the treatment for each condition is different. ADHD requires an increased in CNS alertness while RLS requires an increase in peripheral dopamine receptor activation.
The ADHD Dopamine Deficiency Hypothesis proposes that dopamine deficiency results in insufficient brain activation. This is compensated by a behavioral stimulant, or in simpler terms, need to move. With movement, brain alertness transiently improves helping the child focus and learn. The down side of behavioral stimulant is that it disrupts others. Central Nervous System (CNS) stimulants such as methylphenidate are used as a substitute for the brain activation. By substituting a chemical stimulant for a behavioral stimulant, movement is no longer needed for individual to focus and in turn the excessive movement decreases.
RLS is not a central alerting problem, but rather a peripheral sensory problem. Dopamine activation in the peripheral nervous system acts like a mute on a trumpet to tap down the excessive peripheral sensory input. RLS patients have a decreased activation of dopamine receptors. RLS treatment improves receptor sensitivity by either increasing the amount of dopamine or by increasing the sensitivity of the receptors to the dopamine available. Commonly used agents for RLS are trade named ropinirole and pramipexole.
RLS can mimic ADHD – Both conditions result in an excessive need to move
There is an increased frequency of restless legs syndrome (RLS) in patients diagnosed as having ADHD. Whether this is an error in diagnosis, or two different syndromes in the same patient is difficult to separate. It is worth a try however since some (but not all) ADHD syndrome patients have resolution of their ADHD with correction of their restless legs.
I suggest two approaches in ADHD patients:
- Asking if the restlessness and need to move is confined to the legs or is it a generalized sensation. Individuals with RLS complain of localized restlessness in the legs while individuals with ADHD have generalized sensation to move that is not localized to the legs.
- Checking for an iron deficiency in ADHD patients. Low iron levels can cause a dopamine deficiency. Testing via a serum ferritin level is useful and
easy. A ferritin level under 50 mcg/L suggests that iron replacement may help restless legs.
If a ADHD patient has a low ferritin level and iron replacement corrects the ADHD, the problem was RLS. No improvement with iron replacement suggests another cause for the ADHD syndrome. NOTE: taking excessive iron without a documented iron deficiency can cause damage to the liver. Discuss with your healthcare provider before starting supplemental iron!
Not all patients with RLS have an iron deficiency, however iron deficiency is more common in children than adults. Additional aggravating factors for RLS include taking the certain medications such as Benadryl, antidepressants, and Reglan. Genetics also play a role as RLS can runs in families.
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Written by Steve Zorn, MD. Board Certified Sleep Specialist and Medical Director for Iowa Sleep