Continuous Right Leg Shaking at Night: Evaluation and Management
The most likely diagnosis is Restless Legs Syndrome (RLS), possibly with associated Periodic Limb Movements during Sleep (PLMS), and you should begin evaluation with four specific diagnostic questions, a neurological examination, and serum ferritin testing. 1
Immediate Diagnostic Assessment
The diagnosis hinges on asking four essential clinical questions that establish RLS 1:
- Is there an urge to move the leg accompanied by uncomfortable or unpleasant sensations? (RLS patients describe creepy-crawly, burning, itching, or painful feelings) 1
- Do symptoms begin or worsen during rest or inactivity (such as lying in bed at night)? 1
- Are symptoms partially or totally relieved by movement (walking, rubbing, stretching) for as long as the activity continues? 1
- Do symptoms worsen or only occur in the evening or night? 1
If all four criteria are met, RLS is the diagnosis—polysomnography is not needed in the majority of cases 1
Critical Differential Diagnosis
You must distinguish RLS from two other common nocturnal leg conditions:
Nocturnal Leg Cramps
- Painful, involuntary muscle contractions (typically calf) with no urge to move 2, 3
- Pain is a tightening sensation, not dysesthesias 3
- Relief comes specifically from stretching the affected muscle, not general movement 3
- No circadian pattern 3
Periodic Limb Movement Disorder (PLMD)
- Patient is typically unaware of the movements (bed partner reports kicking/twitching) 2, 3
- Movements are rhythmic, stereotyped (big toe extension, ankle dorsiflexion), lasting 2-4 seconds every 20-40 seconds 2
- Requires polysomnography showing PLMS Index >15/hour in adults 2, 4
- Up to 90% of RLS patients also have PLMS, but PLMS alone without the urge to move is PLMD, not RLS 2, 4
Essential Physical Examination and Laboratory Workup
Perform a thorough neurological examination specifically looking for 1:
- Signs of peripheral neuropathy (reduced sensation, absent reflexes)
- Evidence of radiculopathy
- Vascular assessment (pulses, signs of arterial insufficiency) 3
Obtain serum ferritin level 1:
- Values <50 ng/mL are consistent with RLS and indicate need for iron supplementation 1
- This is the only laboratory test recommended for establishing RLS diagnosis 1
Secondary Causes to Investigate
Evaluate for conditions that cause secondary RLS 1:
- Iron deficiency anemia (most common treatable cause) 1
- End-stage renal disease 1
- Pregnancy 1
- Peripheral neuropathy 1
Medication Review: Common Pitfall
Review all current medications, as several classes exacerbate or trigger RLS 1, 4:
- Tricyclic antidepressants 1, 4
- SSRIs 1, 4
- Lithium 1
- Dopamine antagonists (antipsychotics) 1
- Calcium channel blockers 3
Stopping these medications may resolve symptoms entirely without need for RLS-specific treatment 1
When to Consider Polysomnography
Order sleep study only if 2, 4:
- PLMD is suspected (bed partner reports rhythmic kicking, but patient denies urge to move)
- Sleep disturbance persists despite meeting RLS criteria and receiving appropriate treatment
- Concern for coexisting sleep-disordered breathing 4
Do not order polysomnography for straightforward RLS diagnosis—it adds no value and delays treatment 1
Treatment Implications Based on Diagnosis
If RLS is confirmed:
- Iron supplementation if ferritin <50 ng/mL 1, 5
- First-line pharmacological treatment: gabapentin enacarbil, gabapentin, or pregabalin 2, 5
- Dopaminergic agents may be considered short-term but carry augmentation risk 2
If nocturnal leg cramps:
If PLMD without RLS:
- Treatment may include gabapentin, pregabalin, or levodopa compounds (though evidence is limited) 2
Key Clinical Caveat
The unilateral presentation (right leg only) is atypical for classic RLS, which usually affects both lower extremities 1. This increases the importance of the neurological examination to rule out focal pathology such as radiculopathy or peripheral nerve entrapment 1. However, RLS can occasionally present asymmetrically, and the diagnostic criteria remain the same 1.