What is the differential diagnosis and recommended work‑up for a 30‑year‑old man with leg weakness, fatigue, a constant urge to stretch his legs each morning, and an abnormal gait characterized by stiff straight‑leg walking or excessive knee hyperextension?

Differential Diagnosis and Work-Up

This 30-year-old man's presentation—leg weakness, fatigue, constant urge to stretch his legs in the morning, and abnormal stiff-legged gait—requires urgent evaluation for neuromuscular disorders, particularly Guillain-Barré syndrome (GBS), while also considering restless legs syndrome (RLS) and peripheral neuropathies.

Primary Differential Diagnoses

1. Guillain-Barré Syndrome (Most Urgent)

The combination of leg weakness and abnormal gait (stiff, straight-legged walking) in a young adult is concerning for GBS, which can present atypically with proximal weakness rather than the classic distal ascending pattern 1, 2. GBS is a neurologic emergency with 20% of patients developing respiratory failure 1.

Key features to assess:

• Timing: Rapid progression over days to 2 weeks suggests GBS 1
• Reflexes: Areflexia or hyporeflexia is characteristic 1
• Sensory symptoms: May include "sharp zingers" or numbness in glove-and-stocking distribution 2
• Recent infection: Often preceded by upper respiratory or gastrointestinal infection 1
• Respiratory function: Monitor for dyspnea or increased work of breathing 2

2. Restless Legs Syndrome

The "constant urge to stretch" the legs, particularly in the morning, partially fits RLS criteria, though the timing is atypical (RLS typically worsens at night) 3.

RLS diagnostic criteria (all 4 must be present):

• Urge to move legs with uncomfortable sensations 3
• Symptoms begin or worsen during rest/inactivity 3
• Symptoms relieved by movement (walking, stretching) 3
• Symptoms worse in evening/night 3

Critical caveat: The abnormal gait ("walking on 2 sticks") is NOT consistent with RLS, where physical examination is typically unremarkable 3. This gait abnormality points toward true neuromuscular weakness.

3. Peripheral Neuropathy

Secondary causes including metabolic, toxic, or inflammatory neuropathies can present with leg weakness and sensory disturbances 3, 4.

4. Spastic Gait Disorder

Upper motor neuron lesions can cause stiff-legged gait with knee hyperextension, though this typically presents with hyperreflexia rather than weakness 5.

Immediate Work-Up Algorithm

Step 1: Neurologic Examination (Perform Immediately)

• Deep tendon reflexes: Absent/decreased suggests GBS or peripheral neuropathy; increased suggests upper motor neuron lesion 1, 2
• Muscle strength testing: Document proximal vs. distal weakness pattern 1
• Sensory examination: Pin-prick and vibration testing in glove-and-stocking distribution 1, 2
• Gait observation: Assess for steppage gait (foot drop), spastic gait, or ataxic gait 4
• Cranial nerve examination: GBS can involve facial and bulbar muscles 1

Step 2: Laboratory Testing

If reflexes are absent/decreased or weakness is progressive:

• Lumbar puncture: Cytoalbuminologic dissociation (elevated CSF protein >60 mg/dL with normal WBC) confirms GBS 1, 2
• Electrophysiology: Nerve conduction studies show demyelinating or axonal patterns in GBS 1, 4
• Creatine kinase: Elevated in myopathies 2

If RLS is suspected (but only after excluding neuromuscular causes):

• Serum ferritin: Values <50 ng/mL indicate iron deficiency associated with RLS 3
• Complete metabolic panel: Screen for renal failure (secondary RLS cause) 3

Step 3: Risk Stratification

RED FLAGS requiring immediate hospitalization:

• Progressive weakness over days 1
• Areflexia 1, 2
• Respiratory symptoms or difficulty swallowing 1
• Autonomic instability (blood pressure fluctuations, arrhythmias) 1

If GBS is confirmed:

• Admit to ICU for respiratory monitoring 1
• Initiate intravenous immunoglobulin (IVIG) or plasmapheresis immediately 1
• Monitor for complications including SIADH 2

Common Pitfalls to Avoid

1. Dismissing atypical presentations: GBS can present with proximal rather than distal weakness and with unusual sensory descriptions like "sharp zingers" 2. The classic ascending paralysis is not always present.

2. Attributing everything to RLS: While the urge to stretch fits RLS, the abnormal gait and weakness do NOT. Physical examination in primary RLS is unremarkable 3. The presence of objective weakness mandates neuromuscular evaluation.

3. Delaying lumbar puncture: In suspected GBS, LP should be performed urgently as CSF findings guide treatment decisions 1, 2.

4. Missing secondary causes: Always screen for medications (antipsychotics, SSRIs, tricyclics can worsen RLS), iron deficiency, and renal disease 3.

Treatment Approach

If GBS is diagnosed:

• IVIG or plasmapheresis as first-line treatment 1
• Supportive care with respiratory and cardiac monitoring 1

If RLS is confirmed (after excluding neuromuscular causes):

• Iron supplementation if ferritin <50 ng/mL 3
• Dopamine agonists (ropinirole 0.25 mg or pramipexole 0.125 mg at bedtime) for daily symptoms 3
• Avoid exacerbating medications 3

The abnormal gait pattern described ("walking on 2 sticks" or excessive knee bending) combined with weakness and fatigue strongly suggests a neuromuscular disorder requiring urgent evaluation rather than a primary sleep-related movement disorder like RLS. Proceed immediately with neurologic examination focusing on reflexes and strength testing 1, 2.