Restless Legs Versus Periodic Limb Movements and Iron Status
A 45-year-old woman reports an urge to move her legs in the evening that is worse at rest and relieved by walking. Symptoms began during her second pregnancy and worsened over the past year. She has iron-deficiency anemia (ferritin 12 ng/mL, hemoglobin 10.5 g/dL) from heavy menses. She also reports daytime fatigue and difficulty falling asleep. Her bed partner says she kicks at night. She asks whether she needs a sleep study and whether iron supplements will "cure" her.
1. What is the diagnosis, and how do RLS and periodic limb movements relate?
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The clinical picture is classic RLS: an urge to move, worse at rest and in the evening, relieved by movement. RLS is a clinical diagnosis and does not require polysomnography. Periodic limb movements of sleep (PLMS) are a polysomnographic finding that is common in RLS but also occurs in other conditions and in asymptomatic people; the presence of PLMS does not define RLS, and treating PLMS in isolation is generally not indicated unless it is clinically significant.
2. Does she need a sleep study, and how should her iron deficiency be managed?
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A sleep study is not required to diagnose RLS. It may be considered if another sleep disorder is suspected (e.g., OSA, given fatigue) or if the diagnosis is uncertain. Iron deficiency should be identified and treated-ferritin is low, and iron replacement is appropriate, with oral iron and evaluation of the cause of blood loss; intravenous iron may be considered if oral therapy is inadequate or poorly tolerated. Recheck iron studies after treatment. Iron repletion can improve RLS symptoms, but it is not guaranteed to cure them, and she should be counseled accordingly.
3. If iron repletion does not control her symptoms, what pharmacologic approach would you consider, and what cautions apply?
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First-line pharmacotherapy includes dopamine agonists (e.g., pramipexole, ropinirole) and alpha-2-delta ligands (gabapentin enacarbil, pregabalin). Dopamine agonists can cause augmentation (worsening and earlier onset of symptoms) with long-term use, so alpha-2-delta ligands are often preferred when augmentation risk is a concern. Avoid worsening factors such as sedating antihistamines and dopamine antagonists. Address sleep hygiene and treat any coexisting sleep disorder. Given her anemia, continue iron monitoring.