What is the abnormal Babinski plantar response?

• A. Dorsiflexion of the big toe
• B. Plantarflexion of the toes
• C. Toe curling
• D. Big toe inverts

Answer: (A)

The abnormal Babinski plantar response is when stroking the sole causes the big toe to dorsiflex (bend upward) while the other toes often fan out. This is the hallmark of corticospinal tract dysfunction, an upper motor neuron lesion. Normally in adults, stimulation of the sole elicits toe curling and plantar flexion, not an upward big toe. The upward big toe response reflects a release of primitive reflex pathways that the cortex would normally suppress. It’s important to note that in infants, a similar dorsiflexion can be normal due to immature wiring, but in adults it signals a neurologic problem such as a stroke, MS, or spinal cord injury. The other described responses—plantarflexion of the toes or simple toe curling—are typical normal responses and do not indicate the Babinski sign.