Asterixis

Asterixis

Asterixis is a neurological phenomenon characterized by a jerking or flapping motion of the outstretched hands. It is often described as a "liver flap" because it is commonly associated with severe liver disease, though it can also be a sign of other conditions affecting the brain or metabolic disorders. Asterixis is considered an important clinical sign indicating an altered level of consciousness and metabolic encephalopathy, particularly in the early stages of liver coma.

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Characteristics

Asterixis is a type of negative myoclonus characterized by brief, non-rhythmic interruptions in muscle tone, leading to sudden, brief lapses in posture. In the case of the hands, this results in a flapping motion when the arms are outstretched and the hands are dorsiflexed.

Causes

While asterixis is most commonly associated with hepatic encephalopathy resulting from liver failure, it can also be caused by:

• Renal failure
• Carbon dioxide retention in respiratory failure
• Electrolyte imbalances
• Certain medications that affect the central nervous system

Pathophysiology

The exact mechanism of asterixis is not fully understood, but it is believed to involve disruptions in the diencephalic motor centers, which are responsible for maintaining posture. This disruption is thought to be due to metabolic abnormalities affecting the brain's function.

Diagnosis

Asterixis can be diagnosed through a clinical examination. The "flap test" is conducted by asking the patient to extend their arms and spread their fingers, then observing for the characteristic flapping movements. Additional tests may include blood tests, liver function tests, and imaging studies to identify underlying conditions.

Treatment

Treatment of asterixis focuses on addressing the underlying cause. For example, if asterixis is due to liver failure, treatment may involve measures to reduce ammonia levels, such as lactulose or rifaximin. Management of renal failure, respiratory failure, or electrolyte imbalances is tailored to the specific conditions.

Prognosis

The prognosis for asterixis depends on the underlying cause. If the metabolic disturbance can be corrected, the asterixis and associated symptoms may completely resolve.

See Also

• Hepatic encephalopathy
• Metabolic encephalopathy
• Liver failure
• Renal failure

References

• Adams, R.D., & Victor, M. (1993). Principles of Neurology.
• Ferenci, P., et al. (2002). "Hepatic encephalopathy – Definition, nomenclature, diagnosis, and quantification." Hepatology.

External Links

• National Institutes of Health: Hepatic Encephalopathy
• Medscape: Asterixis

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