Waking with Tingling and Crawling Sensations in Left Leg and Foot
This presentation is most consistent with Restless Legs Syndrome (RLS), which characteristically presents with crawling, tingling, or creepy-crawly sensations in the lower extremities that worsen at night and upon waking, accompanied by an urge to move the affected limb. 1, 2
Primary Diagnostic Consideration: Restless Legs Syndrome
The description of "tingling and crawling" sensations specifically upon waking strongly suggests RLS based on four essential diagnostic criteria 1, 3:
- Uncomfortable sensations described as crawling or creepy-crawly feelings that create a compelling urge to move the lower extremities 1
- Circadian pattern with symptoms worsening at night and toward morning 1, 3
- Symptoms worsen with rest or inactivity (such as lying in bed overnight) 1, 3
- Relief occurs with movement such as walking, rubbing, or stretching 1, 2
The unilateral presentation (left leg only) does not exclude RLS, as symptoms can affect one or both lower extremities 1.
Critical Differential Diagnoses to Exclude
Nocturnal Leg Cramps vs. RLS
The key distinction is the quality of sensation and what provides relief 2:
- Nocturnal leg cramps present with painful, involuntary muscle contractions and tightening sensations (not dysesthesias or crawling), with relief coming specifically from stretching the affected muscle 2
- RLS presents with dysesthesias (crawling, tingling) and an urge to move, with relief from any general movement 2, 3
- Up to 90% of RLS patients have associated periodic limb movements during sleep 2
Peripheral Neuropathy
- Peripheral neuropathy causes sensory deficits that are typically constant rather than circadian, do not improve with movement, and lack the characteristic urge to move 1
- A thorough neurological examination is essential to identify signs of neuropathy or radiculopathy 1, 2
Vascular Causes
- Acute limb ischemia would present with pain, pallor, pulselessness, and poikilothermia—not isolated tingling upon waking 1
- Intermittent claudication from peripheral arterial disease causes cramping with exertion, not at rest 2
Essential Clinical Evaluation
Ask these specific diagnostic questions 2, 3:
- "What exactly does it feel like?" (crawling/tingling suggests RLS; tightening suggests cramps)
- "Does moving around make it better?" (yes for RLS; only specific stretching helps cramps)
- "When during the day is it worst?" (evening/night worsening confirms RLS)
- "Do you have an urge to move your leg?" (present in RLS, absent in cramps)
Perform a focused neurological examination looking for 1, 2:
- Signs of peripheral neuropathy (loss of protective sensation, absent reflexes)
- Signs of radiculopathy (dermatomal sensory loss, weakness)
- Vascular assessment including pulses and signs of arterial insufficiency 2
Obtain serum ferritin level immediately 1, 3, 4:
- Ferritin <50 ng/mL is strongly associated with RLS and warrants iron supplementation 1, 3
- Iron deficiency impairs dopamine transport in the substantia nigra, playing a critical role in RLS pathophysiology 1, 3
- Even ferritin levels between 50-75 ng/mL may warrant supplementation in RLS patients 4
Medication Review
Review all current medications, as several classes exacerbate RLS 1, 3, 4:
- Tricyclic antidepressants
- SSRIs
- Lithium
- Dopamine antagonists (antipsychotics)
These medications should be avoided or alternatives considered if RLS is confirmed 1, 4.
Common Pitfalls to Avoid
- Do not order polysomnography for straightforward RLS diagnosis—it is made clinically without need for sleep studies in most cases 1, 2
- Do not assume electrolyte depletion is the cause without evidence, as this theory is poorly supported 2
- Do not confuse RLS with simple cramps, as this leads to inappropriate treatment (dopaminergic therapy when stretching would suffice) 2
- Do not overlook iron supplementation even when ferritin appears "normal" by general standards—RLS requires higher thresholds (≥50 ng/mL, ideally ≥75 ng/mL) due to brain iron deficiency 3, 4