Asterixis is a neurological disorder that causes a person to lose motor control of certain areas of the body. Muscles — often in the wrists and fingers, although it can happen in other areas of the body — can abruptly and intermittently become lax.
This loss of muscle control is also accompanied by irregular and involuntary jerking movements. For that reason, asterixis is sometimes called “flapping tremor.”
Since certain liver diseases seem linked to asterixis, it’s sometimes called “liver flap” as well. The flapping is said to resemble a bird’s wings in flight.
One way clinicians may test for asterixis is by asking people to stretch out their arms and extend (not flex) their wrists. Repetitive flapping forward may ensue to signify asterixis.
Asterixis on both sides of the body is far more common than unilateral (one-sided) asterixis.
The condition was first recognized nearly 80 years ago, but a lot still remains unknown about it. The disorder is thought to be caused by a malfunction in the part of the brain that controls muscle movement and posture.
Why that malfunction occurs isn’t entirely known. Researchers suspect there may be certain triggers, which include encephalopathies.
Encephalopathies are disorders that affect brain function. Symptoms include:
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.
Impaired liver function is at the root of most cases of asterixis.
When the liver isn’t functioning properly and isn’t able to filter toxins, the toxins can build up in the blood and travel to the brain. This toxicity affects brain function.
Research estimates around 70 percent of people with cirrhosis develop symptoms of hepatic encephalopathy.
Pretty much anything that affects brain function can lead to asterixis. This includes:
A stroke occurs when blood flow to a part of the brain is restricted. This can happen because of a blood clot blocking an artery or because of a narrowing of the arteries due to things like smoking or high blood pressure.
Like the liver, the kidneys also remove toxic materials from the blood. If too many of these toxins are allowed to build up, they can alter brain function and lead to asterixis.
The kidneys and their ability to do their job can be damaged by conditions like:
- high blood pressure
- certain genetic disorders
In Wilson’s disease, the liver doesn’t adequately process the mineral copper. If left untreated and allowed to build up, copper can damage the brain. This is a rare, genetic disorder.
Experts estimate about
- muscle stiffness
- personality changes
Other risk factors
A diagnosis of asterixis is often based on both a physical exam and lab tests:
- Physical exam. A doctor or other healthcare professional (HCP) may ask you to hold your arms out, extend your wrists, and spread your fingers. After a few seconds, a person with asterixis will involuntarily “flap” the wrists downward, then back up. Your HCP may also push against your wrists to prompt the response.
- Blood tests. Your HCP may also order blood tests that look for chemical or mineral buildup in the blood. Blood tests can help diagnose underlying causes of asterixis, such as kidney failure and liver disease.
- Imaging tests. Imaging tests, such as CT or MRI scans, can examine brain function and detect abnormalities or damage.
- Electroencephalogram (EEG). An EEG is used to evaluate the brain’s electrical activity. It can help confirm or rule out encephalopathy and stroke.
When the underlying condition causing asterixis is treated, asterixis generally improves and even goes away entirely.
Encephalopathies of the liver or kidney
Your HCP may recommend:
- Lifestyle and dietary changes. If you’re misusing alcohol or have a kidney-damaging condition like diabetes, your HCP 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.
Your HCP 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.
Your HCP may change the dosage of a medication or switch you to an entirely different drug.
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 HCP 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.
Asterixis isn’t common, but it’s a symptom of a serious and potentially underlying disorder that needs immediate medical attention.
If you’ve noticed any of the flapping tremors characteristic of asterixis or you have any of the risk factors noted above, speak to a doctor or other HCP.
In many cases, when the condition causing asterixis is successfully treated, asterixis can improve or even disappear.