Can a patient with locked-in syndrome have a positive Babinski sign?

Can a Patient with Locked-In Syndrome Have a Positive Babinski Sign?

Yes, patients with locked-in syndrome typically have a positive Babinski sign because the condition involves bilateral ventral pontine lesions that damage the corticospinal (pyramidal) tracts while preserving consciousness.

Neuroanatomical Basis

Locked-in syndrome results from bilateral ventral pontine infarction or injury that disrupts the descending corticospinal tracts. Since the Babinski sign indicates pyramidal tract dysfunction anywhere along its course from the motor cortex through the brainstem and spinal cord, damage at the pontine level will produce this pathological reflex 1.

• The Babinski sign emerges when pyramidal tract dysfunction involves fibers projecting to foot muscle motoneurons, mediated by the extensor hallucis longus 1
• Bilateral corticospinal tract damage at any level—including the pons—produces extensor plantar responses bilaterally 2, 3

Expected Clinical Findings in Locked-In Syndrome

Patients with locked-in syndrome demonstrate the complete constellation of upper motor neuron signs:

• Positive Babinski sign bilaterally (extensor plantar responses) 2, 3
• Hyperreflexia with exaggerated deep tendon reflexes throughout all extremities 2, 3
• Spasticity with velocity-dependent increased muscle tone 2, 3
• Quadriplegia with preserved vertical eye movements and blinking (the defining features that distinguish this from other brainstem syndromes)

Important Clinical Caveat

The Babinski sign may be transiently absent immediately after acute pontine infarction due to spinal shock, despite the presence of pyramidal tract damage 1. This phenomenon of temporary motoneuron inexcitability can create false-negative findings in the hyperacute phase 3, 1.

• Within hours to days, as spinal shock resolves, the Babinski sign will emerge and persist 4, 1
• The absence of the Babinski sign acutely does not exclude pyramidal tract injury 1

Differential Considerations

If a patient with suspected locked-in syndrome lacks a Babinski sign beyond the acute phase, consider:

• Associated peripheral nerve damage, which can mask the central sign 4
• Severe spasticity paradoxically reducing the reflexogenic response (though this is less common) 5, 4
• Alternative diagnosis—the absence of expected upper motor neuron signs should prompt reconsideration of the diagnosis