Ipsilateral Ankle Clonus in Cerebral Infarction: An Uncommon Clinical Phenomenon

Clonus is defined as involuntary, rhythmic muscular contractions caused by persistent damage to descending upper motor
neurons. Clonus can occur in the ankle, patella, triceps surae, wrist, jaw and biceps brachii. It is a marker of hyperreflexia
and indicates disruption of upper motor neurons. These signs, especially when observed together in the right context, signal a
central nervous system insult, which may result from various causes such as vascular issues (stroke), infections (encephalopathy),
congenital conditions (cerebral palsy), hereditary spastic paraplegia, autoimmune disorders (multiple sclerosis), traumatic
injuries (spinal cord insult, chronic myelopathy), severe hepatic failure and serotonin syndrome. In cases of cerebral infarcts,
ankle clonus is typically demonstrated on the contralateral side. However, we have observed a clinical sign of ipsilateral ankle
clonus following acute ischemic stroke. We believe the origin to be compression of the left crus cerebri as part of the Kernohan-
Woltman notch phenomenon. We consider that ipsilateral ankle clonus in acute cerebral infarction is an early indicator of poor
neurological outcome before the sensorium drops and its disappearance indicates a promising prognosis for stroke recovery.