Most Likely Diagnosis: Iron Deficiency (Answer d)
The most likely cause of this patient's insomnia is iron deficiency, manifesting as restless legs syndrome (RLS). The clinical presentation of difficulty falling asleep with a compelling need to get up and move around after going to bed, combined with laboratory evidence of low hemoglobin and MCV values, strongly points to secondary RLS due to iron deficiency 1.
Clinical Reasoning
Key Diagnostic Features Present
This patient exhibits the cardinal features of RLS that distinguish it from other sleep disorders:
- Urge to move with rest/inactivity: She must get up to move around after going to bed, which is pathognomonic for RLS 1
- Circadian pattern: Symptoms occur specifically at night when trying to fall asleep, consistent with RLS's characteristic evening/nighttime worsening 1
- Relief with movement: The need to get up and move around indicates symptom relief with activity, a hallmark of RLS 1
- Sleep-onset insomnia: The 1-2 hour delay in falling asleep is typical of RLS-related sleep disruption 1
Iron Deficiency as the Underlying Cause
Secondary RLS results from medical conditions that have iron deficiency in common, including iron-deficiency anemia 1. The laboratory findings support this:
- Low hemoglobin indicates anemia 1
- Low MCV suggests iron deficiency as the etiology 1
- Iron deficiency impairs dopamine transport in the substantia nigra, which plays a critical role in RLS pathophysiology 1
- The prevalence of RLS increases with age partly due to increasing presence of secondary causes like iron deficiency in the aging population 1
Why Other Diagnoses Are Less Likely
Major depression (option a) is excluded by the patient's explicit denial of depressed mood or loss of interest in hobbies 1. While depression can cause insomnia, it does not explain the compelling urge to move the legs at night.
Obstructive sleep apnea (option b) is unlikely because:
- The patient does not snore, which is a key symptom of OSA 1
- She gets 8 hours of rest once asleep, indicating good sleep maintenance rather than the fragmented sleep typical of OSA 1
- Her BMI and lack of daytime sleepiness argue against OSA 1
Parkinson disease (option c) is excluded by the normal neurological examination showing no tremor or bradykinesia 1. Additionally, Parkinson's typically presents with motor symptoms during the day, not exclusively nocturnal restlessness.
Clinical Pitfalls to Avoid
Do not assume this is simple insomnia or nocturnal leg cramps 2, 3. Nocturnal leg cramps involve painful, involuntary muscle contractions relieved specifically by stretching the affected muscle, not general movement 2, 3. This patient describes an urge to move and get up to walk around, which is characteristic of RLS, not cramps 2, 3.
Do not overlook iron deficiency even with only trace peripheral edema 1. The combination of intentional weight loss and anemia suggests nutritional deficiency that requires investigation 1.
Recommended Next Steps
Check serum ferritin levels immediately 1, 2, 3. Ferritin <50 ng/mL is associated with RLS and warrants iron supplementation 2, 3, 4.
Initiate iron supplementation if ferritin is low, as correction of iron deficiency improves RLS symptoms 1, 4, 5.
Review the patient's antihypertensive medication 1, 4. If she is taking medications that can exacerbate RLS (such as certain antidepressants or dopamine antagonists), consider alternatives 1, 4.