A 68-year-old woman with sleep-onset insomnia.

68-year-old woman, who smokes 1 package of cigarettes daily, presents with fatigue, daytime sleepiness and difficulty falling asleep at night. She reports that, for as long as she can remember , her legs " absolutely needed to move " at bedtime. She has not experienced leg pain or cramps but describes a " prickly feeling under the skin. " Examinations, including neurologic evaluation, reveal no abnormalities. The results of a complete blood count were within normal limits, and her serum ferritin level was 52 (normal 18–160) µg/L. What is the most likely diagnosis? Primary restless legs syndrome is the most likely diagnosis. Restless legs syndrome is a neurologic movement disorder that may adversely affect sleep, and thereby result in daytime fatigue, somnolence and a reduced quality of life. 1–4 This condition has also been associated with hypertension and cardiovascu-lar disease. 4 The pathophysiology of restless legs syndrome is incompletely understood. However, dopamine dysfunction in the central nervous system and iron deficiency in the brain have been implicated. Sleep-onset insomnia is typical. Patients describe an overwhelming urge to move, accompanied by unpleasant sensations in their lower limbs. The sensations are often described as " creeping, " " burning " or " tingling. " These symptoms appear at rest, usually in the evening or at bedtime, and are improved by movement. Patients typically describe voluntarily moving their limbs, stretching, walking or pacing to find relief. Symptoms may also occur during the night, thereby interrupting sleep, and they may occur nightly or on an intermittent basis. 1–4 Restless legs syndrome is common, affecting 5%–15% of the population, yet it is frequently undiagnosed or mistaken for other conditions. Women are affected more often than men, and the prevalence increases with age. 1,3,4 Over half of patients with primary restless legs syndrome have a family history, and a genetic trait with autosomal dominant transmission has been hypothesized. 1,4 Restless legs syndrome may also be associated with other conditions, including diabetes, arthritis, Parkinson disease, chronic renal failure, iron deficiency and pregnancy (secondary restless legs syndrome). 1,3,4 Drugs such as antihistamines, selective serotonin reup-take inhibitors, tricyclic antidepressants and dopamine antagonists can provoke or exacerbate restless legs syndrome. 1 Other conditions with lower limb symptoms that can be confused with restless legs syndrome include akathisia, leg cramps, peripheral neuro-pathy, lumbosacral radiculopathy, vascular diseases and the syndrome of painful legs and moving toes. 1,3,4 Akathisia is characterized by a …