Flapping tremor
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Flapping tremor (asterixis) is a coarse, irregular, non-rhythmic tremor caused by brief lapses in sustained posture, classically seen in hepatic encephalopathy. Now searching the medical library for detailed content.
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Flapping Tremor (Asterixis)
Definition and Nomenclature
Asterixis (from the Greek a- = without, sterixis = fixed position) is the correct term for what is clinically called "flapping tremor." The name is somewhat misleading - it is not a true tremor (which requires rhythmic oscillation), but rather a negative myoclonus: a sudden, brief, arrhythmic lapse in sustained posture caused by involuntary interruption of muscle contraction.
- In hepatic failure, it is also called the "liver flap"
- Adams and Foley first described it in patients with hepatic encephalopathy
"Asterixis differs physiologically from both tremor and myoclonus... it had incorrectly been referred to as a 'negative tremor' or 'negative myoclonus.'" - Adams and Victor's Principles of Neurology, 12e
Pathophysiology
The underlying mechanism involves a cortically generated event:
- A sharp wave originating in the motor cortex precedes a sudden burst of EMG silence lasting 35-200 ms
- This interruption causes the antigravity muscles to briefly lose tone
- Gravity (or muscle elasticity) produces a sudden downward movement - the "flap"
- The patient then corrects the position, sometimes with overshoot
- This cycle repeats arrhythmically, once or several times per minute
This distinguishes it from:
-
True tremor: rhythmic oscillation from alternating agonist/antagonist contractions
-
Myoclonus: brief jerk from active muscle contraction (asterixis is the opposite - from inhibition)
-
Adams and Victor's Principles of Neurology, 12e
How to Elicit (Clinical Examination)
The classic test:
- Ask the patient to hold arms outstretched with wrists dorsiflexed (hands extended, fingers spread) for 15-30 seconds
- Alternatively: rest forearms on bed/chair arms and dorsiflex the hands
- Observe for irregular, arrhythmic downward flapping movements of the hands/wrists
Other methods:
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Ask patient to protude the tongue - it darts in and out
-
Ask patient to close the eyelids - irregular fluttering
-
Ask patient to hold flexed trunk muscles
-
Place hand flat on table and raise the index finger
-
In unresponsive patients: hip flexion-abduction against gravity (hip adductors contract, asterixis becomes prominent)
-
Adams and Victor's Principles of Neurology, 12e; Localization in Clinical Neurology, 8e
Causes
Asterixis is a marker of metabolic or toxic encephalopathy - it is not specific to any single cause.
Classic Causes:
| Cause | Context |
|---|---|
| Hepatic encephalopathy | Most classic; "liver flap" |
| Uremia (uremic encephalopathy) | CKD/AKI - accompanies fine tremor, myoclonus, hyperreflexia |
| Hypercapnia | Type 2 respiratory failure, CO2 narcosis |
| Drug toxicity | Phenytoin, other antiepileptics at toxic levels; some antibiotics; metoclopramide; phenothiazines; gabapentin; opioids (especially meperidine in CKD) |
| Metabolic acidosis | Indistinguishable encephalopathy |
| Alcohol | In context of ALD and hepatic failure |
| Wilson's disease / other metabolic | When encephalopathic |
Focal/Structural (Unilateral Asterixis):
Unilateral asterixis (affecting arm and leg on one side) localizes to a contralateral structural lesion:
-
Anterior thalamic infarction or small hemorrhage (most common)
-
Frontal lobe lesion (ACA infarction)
-
Upper midbrain lesion
-
Parietal lobe lesion
-
Post-stereotaxic thalamotomy
-
Usually transient after stroke
-
Adams and Victor's Principles of Neurology, 12e; Localization in Clinical Neurology, 8e
Asterixis in Hepatic Encephalopathy (Most Important Context)
Hepatic encephalopathy is graded as follows (West Haven Criteria):
| Grade | Features |
|---|---|
| I | Sleep reversal, mild confusion, irritability, tremor, asterixis |
| II | Lethargy, disorientation, inappropriate behavior, asterixis |
| III | Somnolence, severe confusion, aggressive behavior, asterixis |
| IV | Coma - asterixis absent (wanes as coma deepens) |
Key teaching point: Asterixis is present in grades I-III but disappears in grade IV coma - it requires some degree of voluntary muscle contraction to be present.
EEG in hepatic encephalopathy shows slow, high-amplitude triphasic waves.
- The Washington Manual of Medical Therapeutics
Precipitating Factors for Hepatic Encephalopathy:
- GI bleeding (nitrogen load)
- Infection/sepsis
- Constipation, high-protein diet
- Diuretics (hypokalemia, alkalosis)
- Opioids or sedatives
- Azotemia / dehydration
- Medication non-compliance (lactulose)
- TIPS / portosystemic shunts
- Progressive hepatocellular dysfunction
Key Differentials
| Feature | Asterixis | Tremor | Myoclonus |
|---|---|---|---|
| Mechanism | EMG silence (negative) | Rhythmic oscillation | Brief muscle contraction (positive) |
| Rhythm | Arrhythmic | Rhythmic | Arrhythmic |
| Provoked by | Sustained posture | Posture/rest/action | Action/stimulus |
| Context | Metabolic encephalopathy | Essential, Parkinson's, etc. | Anoxic injury, epilepsy |
When mild and low-amplitude, asterixis can resemble 5-6 Hz postural tremor - EMG helps differentiate. - Bradley and Daroff's Neurology in Clinical Practice
Uremic Encephalopathy Context
In CKD/uremic encephalopathy, asterixis accompanies:
- Fine action tremor
- Myoclonus
- Hyperreflexia
The distinction between asterixis and myoclonus in uremia is less clinically important than identifying the metabolic cause, as both can coexist in toxic-metabolic encephalopathy. - Comprehensive Clinical Nephrology, 7e
Summary Points
- Flapping tremor = asterixis = negative myoclonus - not a true tremor
- Mechanism: cortical sharp wave → 35-200 ms EMG silence → gravity pulls limb down → correction → repeated arrhythmically
- Elicited by: wrists extended, arms outstretched (hold 30 seconds)
- Most classic cause: hepatic encephalopathy (liver flap) - but seen in any metabolic/toxic encephalopathy
- Other causes: uremia, hypercapnia, drug toxicity (antiepileptics, antibiotics, opioids)
- Unilateral asterixis → contralateral structural lesion (most often thalamic stroke)
- Present in hepatic encephalopathy grades I-III; absent in grade IV coma
- EEG in hepatic encephalopathy: triphasic waves
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