Asterixis, or flapping tremor, is a clinical sign characterised by the inability to maintain a sustained posture of muscle contraction, resulting in brief, shock-like, involuntary movements. This motor disorder is a type of negative myoclonus, where muscle contractions produce a loss of muscle tone rather than a positive contraction.

Definition and Clinical Significance of Asterixis

Asterixis is typically seen as a bilateral and asynchronous phenomenon, with irregular and variable movements in frequency and amplitude. The clinical sign is often associated with metabolic encephalopathies, particularly hepatic encephalopathy, electrolyte abnormalities, and drug intoxication. Although the exact pathophysiology of asterixis is still unknown, it is believed to be related to impaired function of the diencephalic motor centres and the ascending activating systems associated with arousal.

Causes of Asterixis

It can be caused by a wide variety of metabolic and structural brain disorders, or it can represent an adverse effect of medications.

Metabolic Encephalopathies:

Hepatic Encephalopathy: Asterixis is often associated with liver disease, particularly when ammonia and other toxic metabolites build up in the blood.
Uremic Encephalopathy: Kidney failure can also cause asterixis due to the buildup of toxic substances in the blood.
Carbon Dioxide Retention: Respiratory failure can lead to asterixis due to the buildup of carbon dioxide in the blood.

Electrolyte Abnormalities:

Hypokalaemia: Low potassium levels in the blood can contribute to asterixis.
Hypomagnesemia: Low magnesium levels in the blood can also cause asterixis.

Drug Intoxication:

Antiepileptics: Certain antiepileptic medications, such as phenytoin, valproate, and carbamazepine, can cause asterixis as a side effect.
Antipsychotics: Lithium and clozapine have been linked to asterixis, particularly at therapeutic and toxic plasma levels.
Antibiotics: Ceftazidime has been reported to cause asterixis in rare cases.
Other Medications: Sedatives, such as benzodiazepines and barbiturates, and other medications, like metoclopramide, can also cause asterixis.

Structural Brain Lesions:

Focal Brain Lesions: Asterixis can occur with unilateral lesions in various brain regions, including the thalamus, corona radiate, anterior cerebral artery territory, primary motor cortex, parietal lobe, cerebellum, midbrain, pons, and bilateral structural brain lesions.

Symptoms of Asterixis

Flapping tremors or "flapping" movements:

Asterixis is characterised by sudden, involuntary lapses in muscle contraction, resulting in a flapping or tremor-like movement, often in the hands and wrists.
The flapping motion resembles a bird flapping its wings.

Asynchronous and bilateral presentation:

Asterixis is typically bilateral and asynchronous, meaning the movements are irregular and variable in frequency and amplitude.
In some cases, asterixis may only affect one side of the body (unilateral).

Neurological and cognitive symptoms:

Asterixis is often associated with mental confusion, disorientation, personality changes, and disturbed sleep.
Patients may also experience tremors, recurrent falls, abnormal handwriting or difficulty typing.

Lack of muscle tone:

Asterixis is characterized by the sudden, intermittent loss of muscle tone when attempting to maintain a sustained posture.

Delayed onset:

There may be a latent period between adopting the testing posture and the onset of the flapping tremor, so clinicians are advised to wait at least 30 seconds before concluding the test.

Diagnosis of Asterixis

Asterixis is diagnosed through a combination of physical examination and laboratory tests. The diagnosis involves several steps:

Physical Examination

Hand-Related Methods: The most common way to diagnose asterixis is by having the patient hold their arms, extend their wrists, and spread their fingers. This position is held for at least 30 seconds to ensure accurate diagnosis.
Other Methods: Asterixis can also be diagnosed by testing the legs and feet, although hand-related methods are more commonly used.

Laboratory Tests

Blood Tests: Blood tests identify underlying causes of asterixis, such as kidney failure and liver disease. They can also help diagnose conditions like hypokalemia, hypomagnesemia, and other electrolyte abnormalities.
Imaging Tests: Imaging tests like CT or MRI scans can examine brain function and detect abnormalities or damage that may be contributing to asterixis.
Electroencephalogram (EEG): An EEG evaluates the brain's electrical activity and can help confirm or rule out encephalopathy and stroke.

Differential Diagnosis

Pseudoasterixis: One crucial differential diagnosis of asterixis is pseudoasterixis, which can simulate asterixis by triggering subtle movements.

Treatment of Asterixis

Treatment for asterixis is based on the underlying cause of the disease. The approach involves identifying and addressing the primary condition causing the flapping hand tremor. Here are some treatment options:

Managing Underlying Conditions:

Liver Encephalopathy: Reducing alcohol consumption, managing diabetes, and using laxatives to remove toxins from the body can help alleviate symptoms.
Kidney Encephalopathy: Managing kidney failure through dialysis or a kidney transplant can help resolve asterixis.
Wilson Disease: Medications that stop copper absorption from food and chelating agents to remove copper from body tissues can help treat the condition.

Cardiac Issues:

Weight Loss: Losing weight can help alleviate symptoms where cardiac issues contribute to asterixis.
Quitting Smoking: Quitting smoking can help reduce the risk of cardiac complications that may cause asterixis.
Blood Pressure Medications: Prescribing medications can help manage blood pressure and alleviate symptoms.

Medication-Related Asterixis:

Switching Medications: Switching to a different medication can help alleviate symptoms if the current medication is causing asterixis.

Other Interventions:

EEG and Imaging Tests: These tests can help diagnose the underlying condition and guide treatment.
Dietary Changes: Dietary changes can help manage liver and kidney disease, contributing to asterixis.

Asterixis is a complex condition that requires a comprehensive approach to treatment. Understanding and addressing the underlying cause through appropriate interventions is crucial for effectively managing symptoms.

Reference links:

https://www.ncbi.nlm.nih.gov/books/NBK535445
https://www.osmosis.org/answers/asterixis
https://www.osmosis.org/answers/asterixis
https://www.healthline.com/health/asterixis