Clonus

Definition

Clonus is a series of rhythmic, involuntary muscle contractions elicited by sudden passive stretch. It is most easily tested at the ankle by dorsiflexing the foot and observing for beats of alternating flexion-extension.

Grading

• Sustained clonus (5+ beats): significant upper motor neuron lesion
• Non-sustained clonus (1 to 3 beats): may be normal, especially when tired

Associated Conditions

Upper motor neuron lesions: stroke, spinal cord injury, multiple sclerosis, cerebral palsy. Also prominent in severe preeclampsia/eclampsia as part of generalized hyperreflexia signaling impending seizure.

Nursing Considerations

In preeclampsia, sustained clonus is an ominous sign. Initiate seizure precautions, notify provider, prepare magnesium sulfate. In post-stroke and SCI patients, document clonus as part of neurologic assessment and anticipate antispasmodic therapy (baclofen, tizanidine).

NCLEX Relevance

High-yield in preeclampsia/eclampsia case studies. Recognize clonus as hyperreflexia cue.