Meaning of a Positive Babinski Sign
A positive Babinski sign indicates dysfunction of the pyramidal tract (upper motor neuron) and is always pathological in adults, requiring a thorough neurological evaluation to identify the underlying cause of central nervous system pathology. 1
Clinical Significance
The Babinski sign is a well-established neurological finding that helps differentiate between central and peripheral nervous system disorders. When positive, it manifests as:
- Dorsiflexion of the great toe (upgoing toe)
- Often accompanied by fanning of the other toes
- May include withdrawal of the leg 2
This response occurs following plantar stimulation and represents a disruption of normal inhibitory control from the pyramidal tract.
Underlying Pathophysiology
The positive Babinski sign emerges when there is dysfunction in the pyramidal tract fibers that project to the motoneurons of foot muscles, particularly the extensor hallucis longus 3. This pathological response is part of a broader flexion synergy of the leg that becomes disinhibited with upper motor neuron lesions 4.
Unlike the normal plantar reflex (which is a local S1 reflex resulting in plantar flexion of the toes), the Babinski sign represents part of a defense reflexivity pattern of the lower limbs 5.
Common Associated Conditions
A positive Babinski sign is commonly associated with:
- Stroke (ischemic or hemorrhagic)
- Multiple sclerosis and other demyelinating diseases
- Traumatic brain or spinal cord injuries
- Brain or spinal cord tumors
- Hepatic encephalopathy 1
Clinical Evaluation
When a positive Babinski sign is detected, clinicians should:
Perform a complete neurological examination
Look for other signs of upper motor neuron dysfunction:
- Spastic hypertonia
- Hyperreflexia
- Clonus
- Decreased foot tapping speed 1
Consider appropriate imaging studies:
- CT or MRI of the brain/spinal cord based on clinical suspicion 1
Important Considerations
- A positive Babinski sign may not be present acutely after transverse lesions of the spinal cord or acute brain lesions due to temporary inexcitability of spinal motoneurons 3
- The sign has only fair interobserver reliability (kappa 0.30) compared to other neurological tests like foot tapping speed assessment (kappa 0.73) 1
- The Babinski sign should always be interpreted in the context of the patient's complete clinical picture 1
Elicitation Techniques
The Babinski sign should be triggered preferably in the lateral region of the foot by non-painful stimulation 5. Various methods exist for eliciting this sign, with different sensitivities:
- Classic Babinski method (75% sensitivity in spastic cerebral palsy)
- Gonda-Allen sign (90% sensitivity)
- Allen-Cleckley (82% sensitivity)
- Chaddock (74% sensitivity) 6
The correct interpretation depends less on the method of stimulation and more on assessing the response in the entire leg 4.