2118

Discrete Cortical Infarction With Prominent
Impairment of Thumb Flexion
Yasuo Terao, MD; Hideaki Hayashi, MD; Takemasa Kanda, MD; Hitoshi Tanabe, MD
Background: Intracortical efferent zones in the primary motor cortex for thumb movements, namely
thumb flexion, extension, adduction, and abduction, have been described in Maccaca mullata monkeys but
not in humans. Even recent cortical mapping based on intraoperative monitoring does not provide
information about intracortical efferent zones as it is not ethically possible to search the human motor
cortex extensively by punctate electrodes.
Case Description: A 78-year-old man with discrete cortical embolism over the left central sulcus is
described. Only a mild weakness of his right thumb was observed. Thumb flexion was affected to a greater
degree than thumb extension, adduction, and abduction. The lesion ran along the bottom of the central
sulcus and affected part of the precentral and postcentral gyri on both sides of it. Animal studies in
Maccaca mullata monkeys have shown that the intracortical efferent zones for thumb movement, especially
for thumb flexion, are located in the part of the motor cortex just adjoining the central sulcus that folds
down from the "bank" to the depth of the central sulcus. It was possible to explain the prominent
weakness of thumb flexion if we applied the results of the animal studies.
Conclusions: Our case suggests that the same arrangement of intracortical efferent zones found in
monkeys may also exist in human beings. (Stroke. 1993;24:2118-2120.)
KEY WoRDs * cerebral cortex * embolism * motor activity

P revious studies12 using intracortical stimulation in
Maccaca mullata monkeys have shown that intracortical efferent zones exist in the primary
motor cortex for each of the four thumb movements,
namely, thumb flexion, extension, adduction, and abduction. Recent developments in cortical mapping techniques based on intraoperative monitoring cannot be
applied to humans because it is not ethically possible to
search the human motor cortex extensively by punctate
intracortical electrodes. We describe a case of discrete
cerebral embolism in which prominent weakness of
thumb extension was observed and suggest that the
same cortical organization that has been reported in
monkeys may also exist in human beings.
Case Report
A 78-year-old man without hypertension, hyperlipidemia, diabetes mellitus, atrial fibrillation, or previous
history of myocardial infarction was admitted because
of right hemiplegia and sensory disturbance. On admission he could not raise his right arm from bed. A milder
weakness was noted in his right leg and he could barely
walk with assistance. There were no neuropsychological
signs such as aphasia, impairment of calculating ability,
or disturbance of right-left discrimination. The symptoms gradually subsided during his stay in the hospital
and at the time of discharge only a mild weakness in his
Received May 4, 1993; final revision received July 20, 1993;
accepted July 20, 1993.
From the Department of Neurology, Tokyo Metropolitan Neurological Hospital, Tokyo, Japan.
Correspondence to Dr Yasuo Terao, 3-33-1 Hayamiya, Nerimaku, Tokyo, Japan.

thumb remained. Thumb flexion was affected to a
greater degree (muscle power was 2 by manual muscle
testing [MMT]) compared with thumb extension, adduction, and abduction (muscle power -4 to =4 by
MMT). Weakness was slightly more prominent for
thumb extension (-4 by MMT) than for thumb adduction and abduction (4 by MMT). Because the power of
extension exceeded that of flexion, his right thumb was
kept slightly extended. The power of the other fingers
and extremities was completely normal (only a slight
weakness was noted in the flexion of the index finger).
Dysesthesia was confined to his right thumb and the
skin around the corner of the right side of his mouth,
showing a distribution of cheiro-oral syndrome. Mild
hypesthesia for pin prick and light touch was noted in
his right thumb and the tip of his index finger. He found
great difficulty in identifying items rubbed across the
thumb. The thumb position sense was mildly impaired.
He experienced great difficulty in picking things up
because his fingers felt "slippery" after the attack, and
he thought that this awkwardness could not be explained by the weakness of thumb flexion. Echocardiogram showed no clot in the left atrium.
The episode was considered to be due to cerebral
embolism because computed tomography of the brain
performed 3 days after onset showed a discrete round
area of low density over the left central sulcus with a
spot of high density in the middle (Fig 1). In the
transverse section of magnetic resonance imaging,
which was taken a month after the stroke episode, the
anterosuperior part of the lesion affected the posterior
part of the precentral gyrus that folds down from the
outer surface (or "bank") of the cortex to the bottom of
the central sulcus, whereas the posteroinferior part

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Terao et al Thumb Flexion Impairment in Cortical Infarction

2119

FIG 1. Computed tomographic
taken 3 days after onset of
discrete cortical embolism.
scan

FIG 2. Magnetic resonance imaging of the brain showed a lesion affecting the bottom of the
central sulcus and the adjacent
parts of the precentral and postcentral gyri on both sides of it.
See text for details.

1I

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2120

Stroke Vol 24, No 12 December 1993

involved the postcentral gyrus and the underlying subcortical area. The sagittal section showed the lesion
running along the bottom of the central sulcus and
affecting part of the precentral and postcentral gyri on
both sides of it (Fig 2). Though other small lesions also
existed in the bilateral centrum semiovale, the motor
and sensory symptoms were considered to be due to this
newly appeared lesion because the patient had no
symptoms before the attack. Electromyographic studies
showed no findings suggesting lower motor neuron or
peripheral nerve lesion.
Discussion
Woolsey et a1l mapped the precentral and supplementary motor cortex of the Maccaca mullata monkey
by systemic punctate electrical stimulation and showed
that the stimulation of the posterior part of the motor
cortex that folds down to the bottom of the central
sulcus elicited thumb movement. Though it was not
possible by surface stimulation methods to produce all
four thumb movements, ie, extension, flexion, abduction, and adduction in a single animal, Asanuma and
Ros6n2 succeeded in eliciting these four movements
with weak intracortical stimulation of 10 ,A or less. In
the precentral gyrus the low-threshold efferent zones
for thumb movement were located at the bank to the
depth of the central sulcus; the zones for flexion,
extension, adduction, and abduction were arranged in
this order in the posteroinferior to anterosuperior direction according to the distance from the central
sulcus.

The lesion in our case seemed to affect only part of
the precentral gyrus near the bank to the depth of the
central gyrus. If the results of the above-mentioned

animal experiments are applied to this case, then the
present lesion, which was just adjacent to the central
sulcus, is presumed to affect the cortical zone for thumb
flexion and its efferent fibers more than the zones and
efferent fibers for the other three thumb movements.
The lesion extended rather deeply, but not to the
adjoining white matter, so the cortical efferent zones for
the other three thumb movements and their efferent
fibers were not affected. This may explain the predominant weakness of thumb flexion and the lesser weakness of thumb extension, adduction, and abduction. Our
case suggested that the same arrangement of efferent
zones found in monkeys may also exist in human beings.
Hypesthesia and impairment of two-point discrimination was also noted in the patient's right thumb in the
same area where weakness was noted. This may reflect
the damage to the adjacent part of the postcentral gyrus
folding down to the bottom of the central gyrus. Again,
according to experiments by Woolsey,3 the corresponding region in the left postcentral gyrus of a Maccaca
mullata monkey shows somatotopic representation for
its right thumb and the skin near the corner of the right
side of its mouth.

References
1. Woolsey CN, Settlage PH, Meyer DR, Senger W, Hamuy TP,
Travis AM. Patterns of localization in precentral and 'supplementary' motor area and their relations to the concept of a

premotor area. Res PublAssoc Res Nerv Ment Dis. 1952;30:238-264.

2. Asanuma H, Rosen I. Topographical organization of cortical
efferent zones projecting to distal forelimb muscles in the monkey.
Exp Brain Res. 1972;14:243-256.
3. Woolsey CN. Organization of somatic sensory and motor areas of
the cerebral cortex. In: Harlow HR, Woolsey CN, eds. Biological
and Biochemical Bases of Behavior. Madison, Wis: University of
Wisconsin Press; 1958:63-82.

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Discrete cortical infarction with prominent impairment of thumb flexion.
Y Terao, H Hayashi, T Kanda and H Tanabe
Stroke. 1993;24:2118-2120
doi: 10.1161/01.STR.24.12.2118
Stroke is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 1993 American Heart Association, Inc. All rights reserved.
Print ISSN: 0039-2499. Online ISSN: 1524-4628

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