What is the likely cause and recommended evaluation and management for new‑onset restless‑leg sensations that began concurrently with an acute gastroenteritis episode?

Restless Limbs Concurrent with Acute Gastroenteritis

This presentation does not represent true Restless Legs Syndrome (RLS), as the symptoms fail to meet essential diagnostic criteria, particularly the circadian pattern and chronic course requirements. The temporal association with acute gastroenteritis suggests an alternative etiology requiring focused evaluation.

Why This Is Not RLS

The diagnostic criteria for RLS explicitly require specific patterns that are absent in acute gastroenteritis-associated symptoms 1:

• Circadian pattern is mandatory: RLS symptoms must worsen in the evening/night and improve toward morning 1. Acute gastroenteritis symptoms lack this diurnal variation.

• Chronic course requirement: RLS diagnosis requires symptoms for at least 3 months with onset at least 6 months prior 1. Acute-onset symptoms concurrent with gastroenteritis do not meet this temporal criterion.

• Bilateral involvement is typical: RLS characteristically affects both legs 2, whereas acute metabolic or inflammatory processes may produce asymmetric or variable presentations.

Likely Etiologies in Acute Gastroenteritis Context

Electrolyte Disturbances and Dehydration

The most probable cause is metabolic derangement from fluid and electrolyte losses 1:

• Assess hydration status through skin turgor, mental status, mucous membrane moisture, capillary refill, and vital signs 3
• Obtain serum electrolytes when clinical signs suggest abnormal sodium or potassium concentrations 1
• Muscle cramping, restlessness, and limb discomfort commonly occur with moderate-to-severe dehydration (≥6% fluid deficit) 1

Iron Deficiency Considerations

While iron deficiency is a well-established secondary cause of RLS 1, acute gastroenteritis would not cause immediate iron depletion sufficient to trigger new symptoms. However:

• Check ferritin level if symptoms persist beyond resolution of acute illness 1
• Iron supplementation is indicated for ferritin ≤100 ng/mL in patients with confirmed RLS 4
• In inflammatory bowel disease patients, iron deficiency-associated RLS improved within 4 weeks of supplementation 5

Recommended Evaluation Algorithm

Immediate Assessment (During Acute Illness)

1. Rule out severe dehydration: Check for prolonged skin tenting (>2 seconds), cool/poorly perfused extremities, decreased capillary refill, altered mental status 1

2. Exclude RLS mimics 1:

   • Leg cramps (sudden, painful muscle contractions)
   • Positional discomfort from prolonged bed rest
   • Muscle aches from viral myalgias
   • Venous stasis or leg edema

3. Obtain targeted laboratory studies 1:

   • Serum electrolytes (sodium, potassium, calcium, magnesium)
   • Complete blood count
   • Glucose if altered mental status present

Follow-Up Evaluation (If Symptoms Persist >2 Weeks)

1. Consider post-infectious IBS (PI-IBS): New-onset IBS symptoms can develop following acute gastroenteritis, with symptoms persisting for months 1

2. Reassess for true RLS criteria 1:

   • Urge to move legs with uncomfortable sensations
   • Symptoms begin/worsen with rest
   • Relief with movement
   • Evening/night predominance (critical distinguishing feature)
   • Exclusion of mimics

3. Check iron studies if RLS criteria are met 1, 4:

   • Serum ferritin (target >100 ng/mL)
   • Transferrin saturation (target >20%)

Management Approach

Acute Phase (During Gastroenteritis)

• Prioritize rehydration: Oral rehydration solution is first-line therapy for mild-to-moderate dehydration 3, 6, 7
• Do not delay rehydration while awaiting diagnostic testing 3
• Correct electrolyte abnormalities based on laboratory results 1
• Avoid medications that worsen RLS if symptoms persist: serotonergic antidepressants, dopamine antagonists, antihistamines like diphenhydramine 4

If Symptoms Persist Beyond Acute Illness

• Iron supplementation if ferritin ≤100 ng/mL: ferrous sulfate 325-650 mg daily or every other day 4
• Refer to neurology if true RLS criteria are met and symptoms cause significant sleep disturbance 1
• Consider PI-IBS evaluation if abdominal symptoms persist with altered bowel habits 1

Critical Pitfalls to Avoid

• Do not diagnose RLS based solely on "restless legs" without confirming all five essential criteria, particularly circadian pattern 1
• Do not underestimate dehydration in elderly patients who may not manifest classic signs 3
• Do not attribute symptoms to RLS when they coincide temporally with acute systemic illness—this violates criterion #5 requiring exclusion of symptoms primary to another medical condition 1
• Do not initiate dopaminergic therapy without confirmed RLS diagnosis, as these medications carry 7-10% annual risk of augmentation 4