Asterixis, commonly known as “flapping tremor,” is a neurological sign indicating an inability to maintain a sustained posture. It is characterized by brief, involuntary lapses in muscle contraction. This phenomenon often points to underlying medical conditions affecting the brain’s function, particularly metabolic imbalances. Understanding asterixis involves recognizing its unique physical manifestation, identifying its diverse causes, and knowing how healthcare professionals approach its diagnosis and management.
The “Flapping Tremor” Explained
Asterixis is not a true tremor, but rather a type of negative myoclonus, which describes sudden, brief losses of muscle tone. It is most commonly observed in the hands, appearing when a person extends their arms forward, dorsiflexes their wrists (bends them back), and spreads their fingers, as if pushing against an invisible wall. After a few seconds in this position, the wrists will suddenly “flap” downward due to a momentary loss of muscle tension, then quickly return to the original position. This distinctive movement led to the descriptive name “flapping tremor” or “liver flap”.
While typically bilateral, meaning it affects both sides of the body, asterixis may be more pronounced on one side or asynchronous. Though primarily seen in the hands and wrists, it can also affect other muscle groups, including the legs, feet, tongue, or even the eyelids.
Common Causes of Asterixis
Asterixis is a sign of an underlying issue, most often linked to toxic-metabolic encephalopathies, which are disorders affecting brain function due to metabolic disturbances. The most frequent cause is hepatic encephalopathy, occurring when the liver is unable to filter toxins from the blood efficiently, leading to a buildup of substances like ammonia that impair brain function. Liver diseases such as cirrhosis or hepatitis, which cause scarring and reduce liver efficiency, commonly lead to this condition.
Renal failure, where the kidneys fail to remove waste products, can also cause asterixis due to the accumulation of toxins in the blood that affect brain function. Severe heart failure can also lead to asterixis because the heart may not pump enough oxygenated blood to the brain. Respiratory failure, particularly hypercapnia (excess carbon dioxide in the blood), is another metabolic cause, as elevated CO2 levels can disrupt brain activity.
Certain medications can also induce asterixis as a side effect, especially in individuals with impaired kidney or liver function. Examples include certain medications affecting the nervous system. Less common causes include electrolyte imbalances, such as low potassium or magnesium, and rare genetic disorders like Wilson’s disease, which involves excessive copper accumulation.
How Asterixis Is Diagnosed
The diagnosis of asterixis primarily involves a physical examination. A healthcare professional will ask the patient to extend their arms and dorsiflex their wrists, observing for the characteristic “flapping” motion. This position is held for at least 30 seconds to allow any intermittent loss of posture to become apparent. While the hands are the most common site for assessment, the examination may also include checking for similar movements in the hip joint.
Once asterixis is identified, the diagnostic process shifts to determining its underlying cause. This often involves taking a detailed patient history and conducting various laboratory tests. Blood tests are frequently ordered to check liver function, kidney function, and ammonia levels, as well as to detect electrolyte imbalances. In some cases, imaging studies like CT scans or MRIs may be performed to assess brain function or identify any structural abnormalities that could be contributing to the neurological signs.
Treatment and What to Expect
Asterixis itself is a symptom, not a disease, so there is no direct treatment for the flapping motion. Instead, management focuses entirely on addressing and treating the underlying medical condition responsible for its appearance. For instance, if asterixis is due to hepatic encephalopathy, treatment may involve medications to reduce ammonia levels or lifestyle changes to manage liver disease. For kidney failure, dialysis or other kidney treatments would be implemented.
When asterixis is caused by medication, adjusting the dosage or switching to a different drug can lead to its resolution. The prognosis for asterixis depends heavily on the severity and treatability of the root condition. In many instances, if the underlying cause is successfully managed, the asterixis can improve or even disappear entirely. However, if the underlying condition remains untreated, it can pose significant risks, including potential brain damage or serious injuries from falls, especially if asterixis affects the legs or trunk. It is important to seek medical attention promptly if these symptoms are observed.