What are the differential diagnoses for an adult patient with a history of neurological conditions, presenting with evening spasticity in the spine area?

Differential Diagnoses for Evening Spasticity in the Spine Area

The primary differential diagnosis for an adult with neurological history presenting with evening spasticity in the spine area is restless legs syndrome (RLS) with periodic limb movements (PLM), which is frequently misdiagnosed as spasticity in patients with upper motor neuron conditions. 1, 2

Critical Distinguishing Features

Restless Legs Syndrome with Periodic Limb Movements

• An uncomfortable urge to move the legs with dysesthesias that worsens with rest/inactivity and is relieved by any movement, with symptoms worsening in the evening or at night 1, 3
• Up to 90% of RLS patients have associated periodic limb movements during sleep, which are rhythmic, stereotyped extensions lasting 2-4 seconds occurring every 20-40 seconds 1, 4
• In patients with spinal cord injury or multiple sclerosis, "persistent spasms" inefficiently treated by antispastic drugs are frequently PLM misdiagnosed as spasticity 2
• Relief occurs with any movement but symptoms return when movement stops, distinguishing this from true spasticity 1, 3

True Spasticity (Upper Motor Neuron Syndrome)

• Velocity-dependent increase in muscle tone triggered by rapid passive joint movements (spasticity sensu strictu), or slow passive movements (rigidity), or spontaneous involuntary muscle hyperactivity (dystonia) 5
• Occurs in the presence of central paresis from stroke, multiple sclerosis, spinal cord injury, brain injury, or other neurological conditions 6, 7, 5
• Does NOT have the characteristic urge to move or evening predominance pattern seen in RLS 1
• Resistance is felt during passive movement examination, not primarily patient-reported discomfort 6

Nocturnal Leg Cramps

• Painful, involuntary muscle contractions typically in calf muscles with NO urge to move the legs 1, 3
• Relief comes specifically from stretching the affected muscle, not general movement 1, 3
• Pain is a tightening sensation rather than dysesthesias 1, 3
• Strongly associated with peripheral neuropathy 3

Periodic Limb Movement Disorder (PLMD)

• Requires polysomnography demonstrating PLMS Index exceeding 15 per hour in adults, with clinical sleep disturbance or daytime fatigue, not better explained by another disorder 4
• Can occur independently without RLS symptoms 4
• Movements may cause brief awakenings the patient is unaware of 4

Essential Clinical Evaluation Questions

Ask these specific questions to differentiate:

1. "What does it feel like?" - Cramps produce painful tightening; RLS produces an urge to move with dysesthesias; true spasticity produces stiffness 3

2. "Is it relieved by movement?" - RLS is relieved by any movement but returns when stopping; cramps are relieved by stretching; spasticity persists 3

3. "When does it occur?" - RLS worsens in evening/night and with rest; spasticity is constant or triggered by passive movement 1, 3

4. "Does it occur primarily when lying down or at night?" - If yes, strongly consider PLM rather than spasticity 2

Diagnostic Approach Algorithm

Step 1: Clinical History

• Document timing (evening predominance suggests RLS/PLM vs. constant suggests spasticity) 1
• Assess response to current antispastic medications (failure suggests misdiagnosis as PLM) 2
• Identify urge to move vs. involuntary contractions 1, 3

Step 2: Physical Examination

• Perform passive movement testing to assess velocity-dependent resistance (present in true spasticity, absent in RLS/PLM) 6, 5
• Neurological exam for peripheral neuropathy signs (associated with nocturnal cramps) 3
• Vascular assessment for arterial insufficiency (can cause nocturnal cramps) 3

Step 3: Laboratory Testing

• Check serum ferritin (values <50 ng/mL suggest iron deficiency associated with RLS) 1, 3
• Rule out electrolyte abnormalities if cramps suspected, though poorly supported as primary cause 3

Step 4: Polysomnography

• Obtain nocturnal PSG when spasms prevail at evening, night, or in supine position despite antispastic treatment 2
• This is critical in patients with spinal cord injury or multiple sclerosis with "uncontrolled spasms" 2
• Do NOT order PSG for simple nocturnal leg cramps 3

Common Diagnostic Pitfalls

The most critical pitfall is confusing PLM with spasticity in patients with existing neurological conditions - this leads to inappropriate escalation of antispastic drugs (including intrathecal baclofen pumps) when dopaminergic therapy would be effective 2

Do not assume electrolyte depletion causes nocturnal symptoms without evidence - this theory is poorly supported 3

Do not diagnose PLMD without polysomnography - clinical assessment alone is insufficient 4

Recognize that up to 90% of RLS patients have PLM, but PLM can occur without RLS symptoms 1, 4

Other Differential Considerations

Neurological Mimics

• Neuropathy, akathisia, positional discomfort, and joint discomfort can present with symptoms resembling RLS 1
• Guillain-Barré syndrome presents with progressive weakness over days to 4 weeks with relative symmetry, not isolated evening spasticity 1

Medication-Induced

• Tricyclic antidepressants, SSRIs, lithium, and dopamine antagonists can exacerbate RLS symptoms 3
• Anticonvulsants (carbamazepine, phenytoin) and antihypertensives can cause dizziness mimicking neurological symptoms 1