From the Guidelines
Asterixis, also known as involuntary flapping tremor, is a clinical sign characterized by a negative myoclonus consisting of loss of postural tone, typically associated with hepatic encephalopathy, uremia, and other metabolic disorders 1.
Key Characteristics
- Often present in the early to middle stages of hepatic encephalopathy that precede stupor or coma 1
- Can be observed in other areas, such as the feet, legs, arms, tongue, and eyelids 1
- Not pathognomonic of hepatic encephalopathy, as it can be observed in other diseases, such as uremia 1
Assessment and Diagnosis
- Easily elicited by actions that require postural tone, such as hyperextension of the wrists with separated fingers or the rhythmic squeezing of the examiner’s fingers 1
- Can be assessed using a simple hand-drop test, where the patient is asked to hold their arm straight out with palms down and then suddenly release it, observing for a brief lapse in posture
Treatment
- Primarily focused on addressing the underlying cause, such as administering lactulose or rifaximin for hepatic encephalopathy, with the goal of reducing ammonia levels and alleviating symptoms 1
- Lactulose (15-30 mL orally every 8-12 hours) or rifaximin (550 mg orally twice daily) may be used to treat hepatic encephalopathy 1
From the Research
Definition and Characteristics of Asterixis
- Asterixis is a subtype of negative myoclonus characterized by brief, arrhythmic lapses of sustained posture due to involuntary pauses in muscle contraction 2.
- It is also known as a "flapping tremor" or "liver flap" 3, 4.
- Asterixis is usually asymptomatic and not spontaneously reported by patients, highlighting the importance of actively searching for this sign in the physical exam of encephalopathic patients 2.
Clinical Significance and Associations
- Asterixis has been associated with a wide range of potential causes, both in neurology and general medicine, including hepatic encephalopathy, renal and respiratory failure, cerebrovascular diseases, and certain drugs 3, 2.
- It is not specific to any pathophysiological process but is more commonly reported in certain conditions, such as hepatic encephalopathy 2.
- Asterixis is usually reversible upon treatment of the underlying cause 2.
Pathophysiology and Cortical Activation
- The exact pathogenesis of asterixis remains unknown, but it has been suggested that it may involve the primary motor cortex (M1) 5.
- Cortical activation associated with asterixis has been studied using magnetoencephalography (MEG) and surface EMG, revealing an involvement of M1 in the generation of asterixis 5.
- Asterixis and mini-asterixis (tremulousness) may share common pathophysiological mechanisms, originating in M1 5.