Preserved motor-evoked potentials but without good motor recovery in a patient with decerebrate rigidity.

Abstract

The corticospinal tract is not incriminated in decerebrate rigidity (DR). However, this has not yet been proven in humans. We applied transcranial magnetic stimulation (TMS) in a decerebrate patient to support the hypothesis. A patient suffering from pontine hemorrhage with the fourth ventricular extension was admitted unconscious and in a decerebrate posture. Five days later, she regained consciousness but remained in a decerebrate posture. Motor-evoked potentials (MEPs) to TMS were measured 1 week after she had regained consciousness, and this provoked muscle responses in her hands and feet bilaterally. During the follow-up, the patient's muscle tone became persistently flaccid, although her strength increased to varying degrees in different body and limb muscles. She remained bedridden for 3 years after the stroke and could neither turn on the bed by herself nor perform skilled movements using her hands. The findings of TMS confirmed the animal studies in that the mechanism of decerebrate rigidity did not come through a damage of the corticospinal pathway. This also implies that a preserved corticospinal tract function cannot guarantee a good motor recovery in a stroke patient.

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Case Report
Preserved motor-evoked potentials but without good motor recovery in
a patient with decerebrate rigidity*
Chuen-Der Kaoa,b,c, Kon-Ping Lina,b, Jen-Tse Chena,b,d, Jiun-Bin Changa,b,e, Wan-Yuo Guob,f,
Yung-Yang Lina,b,g, Kwong-Kum Liaoa,b,*
aDepartment of Neurology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC
bDepartment of Neurology, National Yang-Ming University School of Medicine, Taipei, Taiwan, ROC
cDepartment of Neurology, Taichung Hospital, Taichung, Taiwan, ROC
dDepartment of Neurology, Cathay General Hospital, Taipei, Taiwan, ROC
eDepartment of Neurology, Chie-Mei Liouying Hospital, Tainan, Taiwan, ROC
fDepartment of Radiology, Taipei Veterans General Hospital, Taipei, Taiwan, ROC
gDepartment of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan, ROC
Received 1 March 2010; accepted 10 June 2010
Abstract
The corticospinal tract is not incriminated in decerebrate rigidity (DR). However, this has not yet been proven in humans. We applied
transcranial magnetic stimulation (TMS) in a decerebrate patient to support the hypothesis. A patient suffering from pontine hemorrhage with the
fourth ventricular extension was admitted unconscious and in a decerebrate posture. Five days later, she regained consciousness but remained in
a decerebrate posture. Motor-evoked potentials (MEPs) to TMS were measured 1 week after she had regained consciousness, and this provoked
muscle responses in her hands and feet bilaterally. During the follow-up, the patient’s muscle tone became persistently flaccid, although her
strength increased to varying degrees in different body and limb muscles. She remained bedridden for 3 years after the stroke and could neither
turn on the bed by herself nor perform skilled movements using her hands. The findings of TMS confirmed the animal studies in that the
mechanism of decerebrate rigidity did not come through a damage of the corticospinal pathway. This also implies that a preserved corticospinal
tract function cannot guarantee a good motor recovery in a stroke patient.
Copyright ? 2011 Elsevier Taiwan LLC and the Chinese Medical Association. All rights reserved.
Keywords: Decerebrate state; Mobility limitation; Stroke; Tegmentum mesencephali; Transcranial magnetic stimulation
1. Introduction
The technique of transcranial magnetic stimulation (TMS)
hasbeenwidelyappliedintheclinicalinvestigation,1especially
in patients with motor disabilities as a result of cerebrovascular
disorders. TMS is also of prognostic utility, and a preserved
TMS response usually indicates a better outcome.2
The term “decerebrate rigidity” (DR) was first used in 1898
by Sherrington3in describing posture after a prepontine tran-
section. He also concluded that the corticospinal tract could
not be incriminated in either causing or reversing decerebrate
posture after a series of animal studies. To our knowledge,
TMS has not been applied in the study of corticospinal tracts
in DR patients. Here, we report a patient with DR because of
a brainstem hemorrhage. She failed to execute voluntary
movement of her limbs, although her consciousness was clear
and the function of the corticospinal tract was preserved after
the acute stage of DR had passed. We reviewed the mechanism
of DR and the phenomenon of poor motor control even with
preserved function of the corticospinal tract.
*The authors declare no conflicts of interest.
* Corresponding author. Dr. Kwong-Kum Liao, Department of Neurology,
Taipei Veterans General Hospital, 201, Sec. 2, Shih-Pai Road, Taipei 112,
Taiwan, ROC.
E-mail address: kkliao@vghtpe.gov.tw.
1726-4901/$ - see front matter Copyright ? 2011 Elsevier Taiwan LLC and the Chinese Medical Association. All rights reserved.
doi:10.1016/j.jcma.2011.01.005
Available online at www.sciencedirect.com
Journal of the Chinese Medical Association 74 (2011) 37e39
www.jcma-online.com

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2. Case report
A 48-year-old woman suffering from pontine hemorrhage
with the fourth ventricular extension was admitted because of
a sudden change of consciousness. The Glasgow Coma Scale
on admission was 4, the best motor response was 2 (decere-
brate posture), the best verbal response was 1 (no response),
and the eye-opening response was 1 (no response). Neuro-
logical examination revealed a normal light reflex, an absence
of right-eye corneal reflex, and oculocephalic reflex. A
mechanical ventilator was used to support her respiration. DR,
which developed extension of her four limbs with internal
rotation of bilateral arms and plantar flexion, clenching of jaws
and opisthotonos, had been noted since admission, and these
findings were enhanced by pain or pressure stimulations on her
limbs. She regained consciousness 5 days after the stroke
onset and was able to obey simple orders (such as opening and
closing her eyes). Limb movement was limited, and she could
only move the right upper limb slightly. Motor-evoked
potentials (MEPs) to TMS 1 week after she had regained
consciousness showed preserved corticospinal tract responses,
although the onset latencies were delayed and the peak
amplitudes were decreased (Fig. 1).
Three months later, there were residual neurological defi-
cits, with right abducens palsy, right facial and crossed left
hemibody sensory impairment, poor hand dexterities, and
truncal unsteadiness. The patient was able to follow
commands to execute simple tasks, such as moving her
shoulders and flexing and extending her wrists or elbows. She
could not perform some tasks, such as using her hands to write
or to eat with chopsticks, a fork, or a spoon. She could not
maintain a steady sitting position without support, not to
mention an upright posture with support. The muscle response
to TMS became larger along with her muscle strength
improvement, although her muscle tone decreased as hypo-
tonia. She remained in flaccid weakness and did not have
a significant improvement in motor function after 3 years of
follow-up.
3. Discussion
Series of animal studies have revealed that the integrity of
reticular, cerebellar, vestibular, and cortical descending neural
systems is responsible for the development of DR.4Our TMS
findings confirmed these animal studies in that the DR mecha-
nism did not come through a damage of the corticospinal
pathway.TheDRmechanismofourpatientwasmainlybecause
of a lesion involving the rubrospinal pathway and an indirect
disinhibition of vestibulospinal and reticulospinal effects.5
Preserved MEPs to TMS usually indicate a good motor
recovery of stroke patients. However, our patient has remained
bedridden for 3 years after the stroke. In a general sense, the
control of posture and locomotion is based on a spinal central
pattern generator influenced by supraspinal structures and
peripheral afferents. From the original concepts of Kuypers,6
the supraspinal control is divided between two systems:
a fine control of locomotion (the lateral system, including the
corticospinal and rubrospinal tracts) and a provision of
postural support for the fine control (the medial system,
including the reticulospinal and vestibulospinal tracts). During
the control of goal-directed locomotion, selection of a motor
program is performed in the basal ganglia and then reaches the
command centers in the diencephalic locomotion region and
the mesencephalic locomotion region, which can modulate the
spinal central pattern generator for locomotion via the retic-
ulospinal neurons.7In our patient, preserved MEP might
represent certain integrity of the corticospinal tracts. The poor
control of posture and fine voluntary movement might have
come through a locomotion dysfunction by disruption of the
rubrospinal or in part reticulospinal tracts involving the loco-
motion command center at the brainstem level. However,
locomotion failure has been used to describe gait disorders in
humans, and it may not account for the loss of hand dexterity
in our patient.
The concept of incomplete lesion was first proposed by
Dimitrijevic et al,8describing a preserved electrophysiological
function of the corticospinal tract but clinically exhibiting
complete paralysis in spinal man. He supposed that a sub-
stantial number of nerve fibers can survive the trauma but
insufficient to elicit effective contraction of muscles. A similar
concept can be applied to our case, where the lesion involved
the brainstem instead of the spinal cord. The TMS study of our
patient showed residual connectivity of the corticospinal tract,
but she did not have any voluntary movement of the hands and
had poor motor recovery later. This may in part share a similar
“incomplete” mechanism of spinal man.
Loss of dexterity and prolonged flaccid weakness were
noted in our patient. Brainstem lesions may produce cerebellar
diaschisis,9,10which may last 20 years after stroke.11Although
single photon emission computed tomography or positron
emission tomography was not done in our patient, we infer
that she had cerebellar dysfunction because of diaschisis.
Cerebellar dysfunction may decrease human muscle tone and
Fig. 1. The motor-evoked potentials of a 48-year-old patient, who presented
with decerebrate rigidity because of a pontine hemorrhage during the acute
stage and 3 months after stroke onset. Recordings: abductor pollicis brevis and
tibialis anterior.
38 C.-D. Kao et al. / Journal of the Chinese Medical Association 74 (2011) 37e39

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disturb human motor control. Hence, persistent cerebellar
dysfunction because of diaschisis might in part account for her
hypotonia and clumsiness.
In conclusion, DR may occur following a massive, bilateral
cerebral trauma, anoxic damage, or midbrain destructive
lesion, such as the hemorrhagic stroke in our case. Although it
is rare, preserved MEP can occur in humans with DR. Our
case also emphasizes that preserved MEP does not always
indicate a good voluntary movement and motor recovery.
Acknowledgment
This study was supported, in part, by Taipei Veterans
General Hospital (grant no. V99C1-027).
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