What is the most appropriate next step in management for a 68-year-old woman with nighttime calf and foot muscle cramps, normal neurologic exam, normal basic metabolic panel and magnesium, and a serum ferritin of 60 ng/mL?

Iron Supplementation is the Best Next Step

For this patient with a ferritin of 60 ng/mL and symptoms consistent with restless legs syndrome (RLS), iron supplementation is the most appropriate next management step.

Clinical Reasoning

This is RLS, Not Simple Muscle Cramps

The clinical presentation strongly suggests restless legs syndrome rather than simple nocturnal muscle cramps:

• Timing pattern: Symptoms occur specifically during sleep initiation and occasionally wake her from sleep—classic for RLS
• Urge to move: She walks around attempting to relieve symptoms (the defining feature of RLS)
• Lack of daytime symptoms: RLS characteristically occurs at rest/night
• NSAIDs ineffective: This distinguishes RLS from inflammatory or simple cramp conditions
• Normal exam and labs: Excludes neuropathy, electrolyte disturbances, and structural causes

The description of "painful muscle spasms" may be the patient's interpretation of the uncomfortable sensations that characterize RLS, which patients often struggle to describe precisely.

Iron Deficiency is Present by RLS-Specific Criteria

According to the 2025 American Academy of Sleep Medicine (AASM) guidelines, this patient meets criteria for iron supplementation 1:

The AASM Good Practice Statement explicitly states that iron supplementation in adults with RLS should be instituted with oral or IV iron if serum ferritin ≤ 75 ng/mL 1. This patient's ferritin of 60 ng/mL falls below this threshold.

This is critical to understand: RLS iron supplementation guidelines differ fundamentally from general population guidelines. While 60 ng/mL might be considered "normal" in general medicine, it represents iron deficiency in the context of RLS pathophysiology, where brain iron deficiency is a core mechanism 1.

Why Not the Other Options?

Muscle stretches (Option A): The evidence for stretching applies to simple nocturnal leg cramps, not RLS. The Cochrane review found only low-certainty evidence that stretching reduces cramp severity, and this was specifically for muscle cramps—not RLS 2. Given this patient's presentation is consistent with RLS rather than simple cramps, stretching would not address the underlying pathophysiology.

Dopamine agonist (Option B): While dopamine agonists were historically first-line for RLS, the 2025 AASM guidelines have fundamentally shifted the treatment paradigm. The guideline emphasizes that addressing iron deficiency should occur BEFORE initiating other pharmacologic treatments 1. Additionally, dopamine agonists carry significant risk of augmentation (worsening of symptoms), which can be difficult to manage. The guidelines now recommend alpha-2-delta ligands (gabapentin, pregabalin) as first-line pharmacologic therapy when needed, not dopamine agonists.

Implementation Strategy

Step 1: Confirm Complete Iron Studies

While ferritin is 60 ng/mL, you should also check:

• Transferrin saturation (calculated from iron and total iron binding capacity)
• The AASM recommends supplementation if ferritin ≤ 75 ng/mL OR transferrin saturation < 20% 1

Step 2: Initiate Oral Iron Supplementation

For ferritin 60 ng/mL (which is ≤ 75 ng/mL), oral iron is appropriate 1:

• Use ferrous sulfate or other oral iron formulation
• Note: Oral iron absorption is reasonable at this ferritin level (< 75 ng/mL), unlike higher levels where IV iron becomes necessary 1
• Common side effect is constipation—counsel patient accordingly

Step 3: Recheck Iron Studies

• Recheck ferritin in 3 months
• Target ferritin > 75 ng/mL (ideally approaching 100 ng/mL based on guideline discussion) 1

Step 4: Consider Pharmacologic Treatment if Needed

If symptoms persist despite iron repletion or are severely affecting quality of life while waiting for iron to take effect:

• First-line pharmacologic options are alpha-2-delta ligands: gabapentin enacarbil, gabapentin, or pregabalin (all strong recommendations) 1
• Dopamine agonists are no longer preferred first-line due to augmentation risk

Important Caveats

Address exacerbating factors: The AASM guidelines emphasize checking for alcohol, caffeine, antihistamines, serotonergic medications, antidopaminergic medications, and untreated sleep apnea 1. Review her medication list carefully.

Magnesium is not indicated: Her serum magnesium is normal, and evidence shows magnesium supplementation is ineffective for nocturnal leg cramps 3. Even if this were simple cramps rather than RLS, magnesium would not be the answer.

Monitor response: Iron supplementation may take weeks to months to show benefit. If no improvement occurs after adequate iron repletion, reconsider the diagnosis or add pharmacologic therapy.