Clonus is a rhythmic, involuntary muscle contraction and relaxation that occurs when a muscle is stretched. It is often seen in people with neurological disorders, such as multiple sclerosis, Parkinson’s disease, and stroke. Clonus can also be caused by certain medications, such as antidepressants and antipsychotics.
Checking for clonus is a simple procedure that can be performed by a doctor or other healthcare professional. The examiner will first ask the patient to relax and then dorsiflex (bend upward) the patient’s foot. The examiner will then hold the foot in this position and observe for any involuntary muscle contractions. If clonus is present, the foot will shake rhythmically.