What is clonus?

What is clonus?

• A. It is rhythmic muscle spasms
• B. It is a sensation of numbness
• C. It is a muscle atrophy
• D. It is a seizure

Answer: (A)

Clonus is a sign of upper motor neuron involvement, seen as rhythmic, involuntary muscle contractions that occur after a sudden stretch. It happens because the stretch reflex becomes overactive when normal inhibitory signals from the brain are reduced, so the muscle keeps contracting and relaxing in a rapid, repeating pattern after you passively stretch it (often tested by dorsiflexing the foot). This isn’t a single spontaneous jerk or a sensation like numbness or tingling, and it’s not a muscle atrophy or a seizure. Clonus points to CNS‑level hyperreflexia, commonly accompanying conditions such as stroke, spinal cord injury, or multiple sclerosis.

Clonus is a sign of upper motor neuron involvement, seen as rhythmic, involuntary muscle contractions that occur after a sudden stretch. It happens because the stretch reflex becomes overactive when normal inhibitory signals from the brain are reduced, so the muscle keeps contracting and relaxing in a rapid, repeating pattern after you passively stretch it (often tested by dorsiflexing the foot). This isn’t a single spontaneous jerk or a sensation like numbness or tingling, and it’s not a muscle atrophy or a seizure. Clonus points to CNS‑level hyperreflexia, commonly accompanying conditions such as stroke, spinal cord injury, or multiple sclerosis.