Which sign is characteristic of an upper motor neuron lesion?

• A. Weakness
• B. Mild atrophy
• C. Hyperreflexia
• D. Increased tone

Answer: (C)

Upper motor neuron damage removes the brain’s inhibitory control over spinal reflexes, so reflex pathways become overactive. This disinhibition leads to hyperreflexia, a brisk reflex response that is a hallmark of corticospinal tract lesions. While weakness and increased tone (spasticity) often accompany UMN injury, the exaggerated reflexes specifically reflect the loss of supraspinal restraint on the reflex arc. Mild atrophy isn’t typical because the lower motor neurons are still intact, and atrophy usually points to LMN damage or disuse.