A 52-year-old woman comes to the primary care clinic for evaluation of sleep disturbance a… — USMLE Step 2 CK

A 52-year-old woman comes to the primary care clinic for evaluation of sleep disturbance and leg discomfort over the past 3 months. She describes a deep, "crawling" sensation in her calves and thighs that begins almost exclusively when she lies down in bed or relaxes on the couch in the evening. The sensation is accompanied by an irresistible urge to move her legs, and she must pace the hallway for several minutes to find temporary relief. She has no symptoms during the day and sits calmly throughout the examination. Her medical history is significant for bipolar I disorder, hyperlipidemia, and uterine leiomyomas causing heavy menstrual bleeding. Current medications include lithium, lurasidone, and atorvastatin. Vital signs are normal. Neurological examination shows no resting tremor, rigidity, or focal deficits. Laboratory testing reveals a hemoglobin of $11.2 \text{ g/dL}$ , mean corpuscular volume of $76 \text{ fL}$ , and serum ferritin of $18 \text{ ng/mL}$ (Normal: $15-200 \text{ ng/mL}$ ). Which of the following is the most appropriate next step in the management of this patient's sleep-related symptoms?

A
Gabapentin therapy
B
Reduce the dose of lurasidone
Oral ferrous sulfateAnswer
D
Pramipexole therapy
E
Propranolol therapy

Answer

Oral ferrous sulfate

The correct answer is oral ferrous sulfate. This patient's clinical presentation meets the four core diagnostic criteria for Restless Legs Syndrome (RLS): an urge to move the legs, worsening of symptoms during periods of rest or inactivity, partial or total relief with movement, and worsening of symptoms in the evening or night. RLS can be primary (idiopathic) or secondary to other conditions, with iron deficiency being one of the most common and reversible secondary causes. This patient's history of heavy menstrual bleeding and her laboratory results (microcytic anemia with a serum ferritin of

18 \text{ ng/mL}

) confirm iron deficiency. Current clinical guidelines state that for patients with RLS and a fasting serum ferritin level below

75 \text{ ng/mL}

, oral iron supplementation is the most appropriate first-line treatment. Symptomatic pharmacotherapy is generally reserved for patients with normal iron stores or those whose symptoms persist after adequate iron replacement.

Step-by-Step Solution

Analyze the clinical presentation to identify the primary syndrome.

The patient describes an urge to move the legs, worsening at rest, relief with movement, and evening predominance, which fulfills the diagnostic criteria for Restless Legs Syndrome (RLS).

Accurate diagnosis relies on recognizing the four core clinical features of RLS (the URGE criteria).

Differentiate the symptoms from medication-induced side effects.

The lack of daytime restlessness and the prominent circadian pattern distinguish her symptoms from akathisia, an adverse effect of her lurasidone therapy.

Antipsychotic-induced akathisia typically presents as a constant, non-circadian inner restlessness, which requires a different management strategy.

Identify secondary causes of the diagnosed syndrome.

The laboratory findings of microcytic anemia and low serum ferritin (

18 \text{ ng/mL}

) indicate iron deficiency, a major reversible cause of RLS.

Current guidelines recommend evaluating iron stores in all patients presenting with RLS symptoms.

Select the most appropriate initial therapy based on the underlying etiology.

Oral iron supplementation is the indicated next step in management.

For patients with RLS and a serum ferritin level below

75 \text{ ng/mL}

, replenishing iron stores is the first-line treatment before initiating symptomatic pharmacotherapy.

Key Concept

Restless Legs Syndrome (RLS) is clinically diagnosed by an urge to move the legs that worsens at rest and in the evening, and improves with movement. First-line management involves checking a serum ferritin level and prescribing iron supplementation if ferritin is

<75 \text{ ng/mL}

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