Asterixis is an important clinical sign taught to medical students and is often referred to as “hepatic flaps” because it is commonly seen in patients with hepatic encephalopathy. Bilateral asterixis, being nonspecific, is seen in encephalopathies such as uremic encephalopathy, carbon dioxide narcosis, drug-induced sedation, etc. Unlike bilateral asterixis, unilateral asterixis, which is seldom discussed, is almost always associated with contralateral cerebral or an ipsilateral cerebellar pathology. We hereby revisit this important neurological sign and present a patient with isolated unilateral asterixis.
A 53-year-old man presented with an acute-onset behavioral abnormality. After waking up normally one morning, he became irritable and started hallucinating and abusing his relatives. His limb movements were normal. The patient had poorly controlled type II diabetes mellitus and hypertension. On examination, he was abulic. Cranial nerve and motor/sensory examination results were normal. He had flapping tremors in his right wrist and right shoulder [Video 1]. There were no cerebellar signs. His cranial CT scan revealed a left basal ganglia hemorrhagic infarct [Figure 1]. His EEG and somatosensory evoked potentials were normal. He was managed with insulin, antihypertensives, and antiplatelets. His behavior and right-sided asterixis improved over 1 week.
Figure 1: Cranial CT scan showing hemorrhagic infarct involving the left caudate nucleus and putamen
Acute transient behavioral abnormality without motor/sensory deficit is not unusual in patients with basal ganglia (especially caudate) stroke. The only focal sign elicitable in our patient was unilateral asterixis. Unilateral asterixis is always associated with a contralateral structural abnormality of the brain involving the medial frontal lobe (anterior cerebral artery infarcts), parietal lobe, basal ganglia, thalamus, brain stem, and cerebellum. Unilateral asterixis is the most common movement disorder associated with stroke. The pathophysiology of asterixis is not clearly known. It is postulated that multiple extrapyramidal pathways, such as the vestibulospinal, reticulospinal, and rubrospinal tracts, maintain posture and tonic limb movements. These tracts are, in turn, under supratentorial control (ventrolateral thalamus), which, in turn, is intimately connected with the prefrontal, cerebellar, and brain stem tracts (cerebellorubral tracts). Cerebellar lesions produce ipsilateral asterixis due to the crossing of the cerebellorubral tracts in the midbrain. Unilateral asterixis is usually transient suggesting a bilateral supratentorial control over the extrapyramidal pathways. Bilateral asterixis is receptive inattentiveness of incoming information to the parietal lobe/midbrain from the extrapyramidal pathways due to encephalopathy. Occurrence of flaps is associated with appearance of silent periods on surface EMG, which is synchronized to the contralateral central negative sharp waves, suggesting the cortical origin of asterixis.
We conclude that asterixis is a common, useful clinical sign, and unilateral asterixis has a clearly lateralizing value in neurological examination.