A 34-year-old woman recovering from a right-sided stroke is examined. Stroking the sole of her foot from heel to toe along the lateral border produces dorsiflexion of the great toe with fanning of the other toes. This finding indicates:

• A A lesion of the peripheral nerves supplying intrinsic foot muscles
• B Damage to the corticospinal tract at any level above the lumbosacral segments ✓
• C Loss of dorsal column sensory input from the sole
• D It is a normal variant seen in adults with flexible arches

Explanation

The extensor plantar or Babinski response reflects an upper motor neuron lesion anywhere along the lateral corticospinal pathway above the sacral cord segments, including cortex, internal capsule, brainstem, or cord. In adults the descending cortical control suppresses the primitive flexor withdrawal pattern, so plantar stimulation produces flexion of the toes. Peripheral neuropathy causes weak or absent plantar responses, not dorsiflexion. An extensor response is physiological only in infants before myelination of the corticospinal tract matures, roughly under 1 year of age.

Reference: Ganong's Review of Medical Physiology, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.