The Thorndike Laboratory Hospital first noticed the abnormal movements in chronic liver disease. They were referred to as "hepatic flapping" at the time.
James Foley and Praymond Adams first described flapping tremor (in patients with hepatic encephalopathy [Ellul 2017]) in 1949 and referred to it as "asterixis" (Agarwal 2016).
Flapping tremor is a disorder of motor control, a type of negative myoclonus characterized by the inability to maintain a position of tonically active muscles (Agarwal 2016). This loss of tone occurs involuntarily (Manns 2016).
Flapping tremor is one of the negative myoclonias = brief loss of muscle tone (Lazar 2020 / Ibrahim 2022). It can occur unilaterally or bilaterally (Agarwal 2016), is typically asynchronous and variable in amplitude and frequency (Zackria 2022).
Quantitatively, it is differentiated between:
- Grade 1: few, little coarse tremors.
- Grade 2: occasional, occasional coarse tremors (Gerbes 2019).
In addition to flapping tremor, fine-beat tremor with a frequency of 6 - 12 Hz may already occur at the onset of the triggering disease. This is referred to as mini-asterixis (Butz 2015).
Flapping tremor represents a serious neurological sign that can occur in a number of disorders (Agarwal 2016).
There is a brief loss of agonist muscle tone during certain postures of tonically active muscles. This is followed by a compensatory jerk of the antagonistic muscles (Agarwal 2016). These dropouts are caused by involuntary 50 - 200 ms sustained periods of inactivity (Young 1986).
- Execution of the examination:
1. The patient is asked to extend both arms and flex the wrists backward. In the presence of flapping tremor, spontaneous forward movements of the wrist occur (Kasper 2015).
2. The patient lies supine with the knees bent and the feet flat on the support. Now the legs are dropped to the side. Negative myoclonus of the lower extremities occurs in the area of the hip joints, visually visible by movements of the knees (Agarwal 2016).
Bilateral flapping tremor most commonly occurs in the setting of metabolic encephalopathy. Unilateral flapping tremor, which is always suggestive of structural brain lesions, occurs most commonly due to ischemic or hemorrhagic CNS disorders at 95.5% (Agarwal 2016).
Flapping tremor is caused by abnormal function of diencephalic centers (Ploier 2013). However, it is not pathognomonic for any disease (Zackria 2022).
Flapping tremor can occur bilaterally in the context of the following diseases:
- metabolic encephalopathy:
In patients with hepatic encephalopathy, flapping tremor may occur as early as stage II of the West Haven classification (Herold 2022).
- chronic liver failure
- acute fulminant liver failure
- advanced renal failure (Kasper 2015)
- respiratory failure
- azotemia
- Due to drugs such as certain sedatives (e.g., benzodiazepines, barbiturates), antipsychotics (e.g., lithium), anticonvulsants (e.g., carbamazepine, phenytoin), antibiotics (e.g., ceftazidime)
- Bilateral brain injury (Agarwal 2016).
A unilateral flapping tremor is found in:
- focal brain damage in the region of the
- thalamus
- primary motor cortex
- internal capsule
- pons
- cerebellum
- parietal lobe
- Anterior cerebral artery
- Corona radiata (Agarwal 2016).
Phenytoin can unmask a unilateral flapping tremor (Agarwal 2016).
Flapping tremor occurs due to an interruption of electrical activity and results in a sustained contraction of the extensors. This sustained contraction is likely due to intermittent inhibition of the neural system (Tater 2021).
Young and Shahani (1986) suggest that flapping tremor is triggered by basic neuronal or neural system processes.
Both flapping tremor and mini-asterixis involve the contralateral primary motor cortex, and therefore a common pathophysiology may be inferred (Butz 2015). The exact pathophysiology has not yet been elucidated, but several theories exist (Zackria 2022).
Therapy consists of treatment of the underlying condition.
The flapping tremor itself is hardly treatable and proves to be most resistant to therapy (Chandarana 2021).
Flapping tremor has prognostic value in the setting of chronic liver disease:
It is rarely observed in early or advanced hepatic encephalopathy. It disappears with the onset of hepatic coma (Agarwal 2016).