Restless Leg Syndrome (RLS) and Periodic Limb Movement Disorder (PLMD): Tests and Diagnosis

What tests are used to diagnose RLS and PLMD?

Doctors often order a blood test to measure iron (serum ferritin) levels for patients who may have RLS. Studies have found associations between low stores of iron in the body and increased RLS symptoms, probably because of iron’s important role in brain dopamine function.

Similarly, iron deficiency can cause or worsen RLS in children and adolescents, even when the deficiency is not severe enough to cause anemia. A ferritin level of less than 50 mcg/L, which may even be in the low-normal range, indicates a potential problem.

A diagnosis of PLMD is based on three criteria:

  • Periodic limb movements during sleep exceeding norms for age ( more than 5 per hour for children)
  • Clinical sleep disturbance and
  • The absence of another primary sleep disorder or underlying cause (including RLS)

In a child with RLS, the physical exam is usually normal. Family history is important because there is a 50% chance of passing the RLS trait on to children if a parent has RLS.

How do providers at Children’s Hospital Colorado make a diagnosis?

Medical professionals have developed criteria for diagnosing RLS in children ages 2 through 12 years. with definite, probable or possible RLS:

  • Definite RLS: A child feels an urge to move the legs that begins or worsens with sitting or lying down and is partially or totally relieved by movement. The urge is worse in the evening or night than during the day, or occurs exclusively in the evening or nighttime hours. Children describe the discomfort using their own words, such as “oowies, tickle, tingle, static, bugs, spiders, ants, boo-boos, want to run, a lot of energy in my legs,” etc. There is a clinical sleep disturbance for age. A biological parent or sibling has RLS. A sleep study has documented a periodic limb movement index of 5 or more per hour of sleep.
  • Probable RLS: There is an urge to move the legs and the move begins or worsens with sitting or lying down. The urge to move is partially or totally relieved by movement, and the child has a biological parent or sibling with definite RLS.
  • Possible RLS: The child has PLMD and a biological parent or sibling has definite RLS, but the child does not meet the criteria for definite or probable childhood RLS.

Adolescents (13 years and older) are evaluated with the adult criteria.