What is the term for a series of involuntary muscular contractions and relaxations seen in upper motor neuron lesions?

• A. Gait
• B. Clonus
• C. DTRs
• D. FNF test / FTN test

Answer: (B)

Clonus is the term for a series of involuntary, rhythmic muscle contractions and relaxations that occur after a sudden stretch, most often at the ankle. It happens when upper motor neuron lesions remove the brain’s dampening effect on spinal reflexes, so a quick stretch keeps triggering motor neurons to fire in a repetitive cycle. This rhythmic, beating response is a hallmark that helps distinguish upper motor neuron–related signs from a simple, single brisk reflex. Gait describes walking, not this specific sign; deep tendon reflexes can be brisk in UMN disease but do not produce the repeated contractions that define clonus; other exam maneuvers refer to different tests and are not the same phenomenon.