Second edition

03.qxd 3/10/08 9:32 AM Page 97
typically tested for by asking patients to hold their arms
straight to the front with the hands hyperextended at the
wrist as far back as possible, and holding that position for
at least 30 seconds. When asterixis is present, there will be
arrhythmically occurring ‘flaps’ of the hands down, followed,
after a brief, but distinct, moment, by recovery back
to the hyperextended position; although in most cases both
hands will ‘flap’ down simultaneously, occasionally asterixis
will be strictly unilateral, a finding with, as discussed
below, considerable diagnostic significance. In cases where
patients are unable to hold their arms forward, an alternative
approach to eliciting asterixis involves having the
patient rest the arms prone on the bed and then asking him
or her to hyperextend the hands off the bed, again holding
that position for at least 30 seconds.
Etiology
As noted in Table 3.12, asterixis may be seen in the course of
a metabolic encephalopathy, such as hepatic encephalopathy,
as a side-effect to various medications, and during the
course of stroke due either to infarction or hemorrhage.
From a diagnostic point of view it is critical to keep in mind
whether the asterixis is bilateral or unilateral. Asterixis
occurring in the course of a metabolic encephalopathy or as
a side-effect is always bilateral; asterixis occurring as part of
Table 3.12 Causes of asterixis
Metabolic encephalopathy
Hepatic encephalopathy (Adams and Foley 1949, 1953; Read
et al. 1961)
Uremic encephalopathy (Mahoney and Arieff 1982; Raskin and
Fishman 1976; Tyler 1965)
Respiratory failure (Austen et al. 1957; Bacchus 1958)
Medication side-effect
Phenytoin (Chi et al. 2000; Murphy and Goldstein 1974)
Carbamazepine (Rittmannsberger and Lebihuber 1992)
Gabapentin (Babiy et al. 2005)
Pregabalin (Heckmann et al. 2005)
Valproate (Bodensteiner et al. 1981)
Lithium (Stewart and Williams 2000)
Levodopa (Glantz et al. 1982)
Clozapine (Rittsmannberger 1996)
Trimethoprim/sulfamethoxazole (Dib et al. 2004)
Ifosfamide (Meyer et al. 2002)
Metrizamide (Bertoni et al. 1981)
Infarction or hemorrhage
Cortex
Basal ganglia
Internal capsule
Thalamus
Midbrain
Pons
Cerebellum
3.13 Mirror movements 97
a stroke syndrome, although occasionally bilateral, is, in the
vast majority of cases, unilateral. Thus, if a patient has unilateral
asterixis, the presumption must be that it is occurring
secondary to infarction or hemorrhage in one of the areas
described below.
Of the metabolic encephalopathies, hepatic encephalopathy
is so commonly associated with asterixis that, for a
time, the term ‘liver flap’ was used as a synonym for asterixis.
Uremic encephalopathy is almost always associated
with asterixis; in cases of respiratory failure, however, it
may be less common.
Of the medications capable of causing asterixis as a sideeffect,
the AEDs and lithium are the most frequent offenders,
with the other agents only uncommonly being
implicated. Metrizamide myelography may be followed by
a delirium accompanied by asterixis.
Infarction or hemorrhage of the cortex (most commonly
the frontal cortex), basal ganglia, internal capsule,
thalamus, midbrain, pons, and cerebellum may each cause
asterixis, which, as noted above, is generally unilateral, and,
with the exception of cerebellar lesions, is contralateral to
the lesion (Degos et al. 1979; Kim et al. 2001b; Rio et al.
1995; Stell et al. 1994; Tatu et al. 2000). Notably, of all these
areas, it is the thalamus that is most commonly involved.
Differential diagnosis
Myoclonus is distinguished by the fact that it represents
not an abrupt loss of tone with a ‘flap’ down but rather an
abrupt gain of tone with a resultant ‘jerk’. Tremor is distinguished
by the presence of a more or less rhythmic oscillatory
movement secondary to alternating contraction of
agonist and antagonist musculature.
Treatment
Treatment is directed at the underlying condition; symptomatic
treatment is not required.
3.13 MIRROR MOVEMENTS
Mirror movements are normal in early childhood and may
persist into adult years; they may also be seen in certain
disorders, for example stroke with hemiparesis.
Clinical features
Mirror movements are typically seen in the hands, and
may in some cases involve the arm. They may be elicited by
asking patients to perform a fine motor task with one
hand, for example sequential finger–thumb apposition. As
the patient performs the maneuver, simply observe the
other hand for the mirrored movement. With hemiparetic
patients, a simpler strategy involves telling the patient you