Which finding is characteristic of an upper motor neuron lesion?

• A. Fasciculations
• B. Hyperreflexia with Babinski
• C. Flaccid paralysis
• D. Muscle atrophy

Answer: (B)

Upper motor neuron lesions disrupt the brain’s inhibitory control over the spinal cord, leading to a pattern of increased reflexes and abnormal plantar responses. The hallmark here is hyperreflexia paired with a Babinski sign. When the corticospinal (pyramidal) tract is damaged, the loss of descending inhibition causes the alpha motor neurons to become overly excitable, so reflexes are amplified and an extensor plantar response appears (Babinski).

Other signs point to different problems. Fasciculations are spontaneous muscle twitches from irritation or death of lower motor neurons. Flaccid paralysis and muscle atrophy reflect loss of lower motor neuron input or denervation, so tone is diminished and muscles waste away.