What are the causes of bilateral plantar extensor?

Causes of Bilateral Plantar Extensor Response

The most common cause of bilateral extensor plantar responses (Babinski sign) is upper motor neuron lesion affecting the corticospinal tracts bilaterally, typically from conditions affecting the brain or spinal cord above the lumbar region. 1

Primary Causes

Neurological Conditions

• Bilateral cerebral lesions:

  • Stroke affecting both hemispheres
  • Traumatic brain injury with bilateral involvement
  • Brain tumors affecting both hemispheres or midline structures

• Spinal cord disorders:

  • Spinal cord compression (tumors, herniated discs)
  • Spinal dural arteriovenous fistula 2
  • Transverse myelitis
  • Multiple sclerosis with spinal involvement
  • Spinal cord trauma

• Neurodegenerative disorders:

  • Motor neuron disease/ALS
  • Advanced multiple sclerosis
  • Hereditary spastic paraplegia

Metabolic and Toxic Conditions

• Severe hypoxic-ischemic brain injury
• Hepatic encephalopathy
• Uremic encephalopathy
• Drug toxicity (particularly anticonvulsants at toxic levels)

Diagnostic Significance

The bilateral extensor plantar response is a key finding in the diagnosis of upper motor neuron lesions. According to the Guillain-Barré syndrome diagnostic criteria, extensor plantar responses are actually listed as features that cast doubt on this diagnosis, highlighting their importance in differentiating central from peripheral nervous system disorders 1.

Clinical Correlation

When evaluating bilateral plantar extensor responses, it's important to assess:

1. Associated neurological signs:

   • Increased muscle tone/spasticity
   • Hyperreflexia
   • Clonus
   • Weakness pattern (upper motor neuron pattern)

2. Distribution of findings:

   • Symmetrical vs asymmetrical
   • Involvement of upper extremities
   • Sensory level (if present)

Expanded Reflexogenic Zone

In advanced pyramidal dysfunction, the receptive field for eliciting the Babinski response may extend beyond the sole to include the leg or thigh. This phenomenon, known as "kinaesthetic extensor plantar response," indicates severe upper motor neuron dysfunction 2.

Special Considerations

1. In children: The extensor plantar response may be normal in infants up to 12-18 months of age due to incomplete myelination of the corticospinal tracts. In children with cerebral palsy, the Gonda-Allen method (90% sensitivity) is more sensitive than the classic Babinski method (75% sensitivity) for detecting extensor toe signs 3.

2. Crossed extensor plantar response: In some cases, stimulation of one sole may produce an extensor response in the contralateral foot, which can indicate specific lesions in the paracentral lobule 4.

3. False positives: Withdrawal responses due to pain, cold feet, or ticklishness can be mistaken for true Babinski signs. Ensure proper technique with a blunt object using moderate pressure.

Clinical Pitfalls to Avoid

1. Misinterpreting withdrawal responses: A true Babinski sign involves dorsiflexion of the great toe with fanning of the other toes, not just withdrawal of the foot.

2. Overlooking bilateral findings: When bilateral extensor responses are present, focus on investigating central nervous system pathology rather than peripheral causes.

3. Ignoring context: In diabetic patients with peripheral neuropathy, the absence of plantar responses may not be clinically meaningful due to sensory loss 1.

4. Failing to correlate with other UMN signs: Isolated extensor plantar responses without other upper motor neuron signs should prompt careful reassessment.

By systematically evaluating bilateral plantar extensor responses in the context of other neurological findings, clinicians can effectively narrow down the differential diagnosis and guide appropriate neuroimaging and further workup.