Does a positive Babinski sign indicate a spinal injury above the T6 level?

Babinski Sign and Spinal Cord Injury Level

A positive Babinski sign does not specifically indicate a spinal cord injury above T6, but rather indicates upper motor neuron dysfunction that can occur with any lesion affecting the corticospinal tract, regardless of the specific level of injury.

Understanding the Babinski Sign

The Babinski sign is a pathological reflex characterized by dorsiflexion of the big toe and fanning of the other toes when the sole of the foot is stimulated. It has several important characteristics:

• It indicates dysfunction of the pyramidal tract (corticospinal tract) 1
• It has fair interobserver reliability (kappa 0.30) compared to other upper motor neuron tests like foot tapping speed (kappa 0.73) 2, 3
• It is always pathological in adults when present 3
• It may not appear immediately after acute spinal cord injury due to temporary inexcitability of spinal motoneurons 1

Relationship to Spinal Cord Injury Level

The presence of a Babinski sign in spinal cord injury:

• Does not depend on the specific level of lesion (above or below T6) 4
• Is more closely associated with the presence of spasticity rather than the level of injury 4
• May be absent in complete spinal cord injury patients (51% of subjects in one study) despite upper motor neuron damage 4

Factors Affecting Babinski Sign in Spinal Cord Injury

Several factors influence whether a Babinski sign will be present in spinal cord injury:

• Spasticity: Most patients with a positive Babinski sign also present with high spastic muscle tone, while those with a negative sign show low or absent spastic tone 4
• Associated peripheral nerve damage: In many SCI subjects, absence of the Babinski sign is due to peripheral nerve damage 4
• Medications: Antispasmodic medications like Baclofen can eliminate the Babinski sign along with other spastic signs 4
• Timing after injury: The sign may not be present acutely after transverse lesions of the spinal cord due to temporary inexcitability of spinal motoneurons 1

Clinical Implications

When a positive Babinski sign is detected:

• It should trigger a thorough neurological evaluation to identify the underlying cause of upper motor neuron dysfunction 3
• Look for other signs of upper motor neuron dysfunction, such as spastic hypertonia, hyperreflexia, clonus, and decreased foot tapping speed 3
• Consider imaging studies (CT or MRI of the brain/spinal cord) based on clinical suspicion 3
• Direct treatment at the underlying cause, not just the presence of the sign itself 3

Common Pitfalls in Interpretation

• Relying solely on the Babinski sign for diagnosis of upper motor neuron lesions (consider foot tapping speed, which has better reliability) 2
• Failing to consider associated peripheral nerve damage that may mask the Babinski sign in spinal cord injury 4
• Not accounting for the temporary absence of the sign in acute spinal cord injury 1
• Overlooking the negative correlation between extreme spasticity and Babinski sign positivity in conditions like cerebral palsy 5

The Babinski sign should always be interpreted in the context of the patient's complete clinical picture, considering other neurological signs and medical history.