Asterixis

Asterixis is a clinical sign that describes the inability to maintain sustained posture with subsequent brief, shock-like, involuntary movements. This motor disorder is myoclonus characterized by muscular inhibition (whereas muscle contractions produce positive myoclonus).

Asterixis is an uncommon but significant sign in central nervous system (CNS) disorders . Bilateral asterixis is usually due to metabolic encephalopathies. The classic description has been in hepatic diseases but other causes can commonly cause asterixis including azotemia and respiratory disease.

Asterixis can be elicited on physical examination by having the patient extend their arms, dorsiflex the wrists, and spreading the fingers (similar to pushing against a wall) with their eyes closed. This is used to test for the “flap” at the wrist and is the most common method of assessment.

Asterixis is the inability to maintain posture due to a metabolic encephalopathy. This can be elicited on physical exam by having the patient extend their arms and bend their hands back. With a metabolic encephalopathy, the patient is unable to hold their hands back resulting in a “flapping” motion consistent with asterixis. It can be seen in any metabolic encephalopathy e.g. chronic kidney failure, severe congestive heart failure, acute respiratory failure and commonly in decompensated liver failure.

Causes:

Some types of encephalopathy that can result in asterixis are:

• Hepatic encephalopathy. Hepatic refers to the liver. The liver’s main function is to filter toxins from the body. But when the liver is impaired for any reason, it may not remove toxins efficiently. Consequently, they can build up in the blood and enter the brain, where they disrupt brain function.
• Metabolic encephalopathy. A complication of liver and kidney disease is metabolic encephalopathy. This occurs when too much or too little of certain vitamins or minerals, such as ammonia, cross the blood-brain barrier, causing neurological misfirings.
• Drug encephalopathy. Certain medications, such as anticonvulsants (used to treat epilepsy) and barbiturates (used for sedation), can affect brain responses.
• Cardiac encephalopathy. When the heart doesn’t pump enough oxygen throughout the body, the brain is affected.

Treatment:

When the underlying condition causing asterixis is treated, asterixis generally improves and even goes away entirely.

Encephalopathies of the liver or kidney:

Your doctor may recommend:

• Lifestyle and dietary changes. If you’re misusing alcohol or have a kidney-damaging condition like diabetes, your doctor can talk to you about reducing your health risks.
• Laxatives. Lactulose in particular can speed the removal of toxins from the body.
• Antibiotics. These drugs, like rifaximin, reduce your gut bacteria. Excessive gut bacteria can cause too much of the waste product ammonia to build up in your blood and alter brain function.
• Transplants. In severe cases of liver or kidney damage, you may need a transplant with a healthy organ.

Metabolic encephalopathy:

Your doctor will likely advise dietary changes, taking drugs that will bind to the mineral to help remove it from the body, or both. It will depend on which mineral is overabundant in your bloodstream.

Drug encephalopathy:

Your doctor may change the dosage of a medication or switch you to an entirely different drug.

Cardiac encephalopathy:

Getting any underlying heart conditions under control is the first step. That may mean one or a combination of the following:

• losing weight
• quitting smoking
• taking high blood pressure medication

Your doctor may also prescribe ACE inhibitors, which widen arteries, and beta-blockers, which slow the heartbeat.

Wilson’s disease:

Your doctor may prescribe drugs such as zinc acetate, which prevents the body from absorbing copper in the food you eat. They may also prescribe chelating agents like penicillamine. It can help excrete copper out of tissues