The locked-in syndrome (LIS) denotes
quadriplegia owing to bilateral transsection of
pyramidal tracts at the level of pons or
cerebral peduncles. In a
previous article, several voluntary motor
phenomena occurring in LIS were described. Oral
motor patterns were not observed in these cases
and to our knowledge have been mentioned only
once in the literature. This was in contrast to
observations in cerebral malformations and in
severe posttraumatic brain damage. Since our
interest was attracted to this contradiction, we
were able to observe three patients with LIS in
whom oral automatisms occurred secondary to
local (oral and perioral) and general
stimulation.
REPORT OF CASES
Case 1. A 59-year-old woman had been
hypertensive for ten years. She had experienced
two episodes of transient neurological deficits
followed by complete recovery. She was admitted
because of sudden left-sided weakness and
slurred speech. Neurological deficits indicated
extensive brainstein involvernent. The speech
was dysarthric, both eyes were deviated to the
left, and nystagmus was observed in a vertical
plane. Quadriparesis was accentuated in the
right extremities. Plantar responses were
extensor. Secondary to noxious stimulation
extensor posturing occurred on the right side
and flexor posturing on the left.
The next day, neurological symptoms had
deteriorated. Except for vertical eye movements,
the patient was completely paralyzed, including
facial movements. She was alert, and by
blinking, a communication code could be
established. Seven days after admission, the
patient remained in a nearly classic locked-in
condition. At this time several involuntary
motor phenomena could be observed. Bilateral
extensor posturing and a grimacing pain reaction
occurred after noxious stimulation. Sighing and
groaning were noted but were not linked to any
exogenous stimulus. With oral and perioral
stimulation, sucking and chewing could be
elicited. These movements showed a stereotyped
sequence and could be regularly triggered,
although diminution of response was evident with
repeated stimulation. The response could also be
elicited with noxious stimuli applied at the
shoulder fold, but the response was less
constant.
The EEC was minimally abnormal with sporadic
theta waves over both temporal regions. The 8-
to 10-eps alpha rhythm was blocked by eye
opening. A computed tomographie (CT) scan was
normal. Cerebral angiography disclosed severe
sclerotic abnormalities of both carotid arteries
and a complete occlusion of the basilar
artery.
Case 2. A 51-year-old woman suffered
from severe headache three days before
admission. She was admitted in stupor with small
pupils, skewed deviation of the eyes, extensor
rigidity of all four extremities, and upgoing
toes bilaterally. Aroused, she opened her eyes
and moved them in a vertical plane. Five days
later the condition had deteriorated. Except for
vertical eye movements and weak movements of the
left hand, she was completely paralyzed. Ocular
bobbing was noted. Although some elouding of
consciousness was evident, communication by eye
blinking was possible. The patient denied
disturbance of tactile and painful sensibility
in the face, but left-sided hemihypaesthesia was
signaled below the trigeminal level.
Oral and perioral stimulation produced
chewing automatisms. Stimulation of other parts
of the body were not effective. Oral movements
never occurred spontaneously.
The EEG was moderately abnormal with
intermittent 3- to 5-eps activity over both
temporal regions. An 8- to 10-eps alpha rhythm
was present and blocked by eye opening. A CT
scan demonstrated a small hypodense area within
the pons extending upward into the midbrain,
more to the left. The clinical diagnosis was
"incomplete LIS due to an infarct within the
pons." Her condition was unchanged 20 days after
admission.
Case 3. A 79-year-old housewife was in
good condition until one month before admission,
when attacks of dizziness accompanied by raised
BP occurred. She was admitted because of rapidly
developing right-sided hemiparesis and slurred
speech. The next day she was immobile except for
vertical gaze movements. She was able to use
these movements for communication. Ten days
later, her neurological condition has slightly
improved. Inconspicuous opening of the mouth was
possible. In contrast to the small extent of
voluntary movements, automatic sighing and
facial expression of pain occurred secondary to
noxious stimulation. Prolonged chewing was
observed after perioral stimulation.
The EEG was slightly abnormal, with a 6- to
7-eps basic rhythm that was blocked by eye
opening. Some diffuse 2- to 3-eps activity was
interspersed. Spinal fluid and CT sean were
normal.
A clinical diagnosis of "classical LIS due to
a pontine infarct" was made. The patient died 18
days after admission. Autopsy results disclosed
atherosclerosis of the basilar and both
vertebral arteries. An infarct 1 cm in diameter
was found within the ventral pons.
COMMENT
As shown by observations in complex partial
epileptic seizures and by stimulation
experiments in man, the central representation
of oral automatisms are located bilaterally in
the most caudal part of the precentral gyrus and
near the amygdaloid nucleus. Oral automatisms
consist of sucking, chewing, and swallowing and
may occur reflexlike without participation of
more central structures.
From animal experiments and clinical
observations a primordial system of coordination
for mastication can be assumed in the medulla
oblongata, including the motor nuclei of the
fifth, seventh, and twelfth cranial nerves. Oral
automatisms are most easily elicited by
stimulation of the mucous membrane of the lips,
tongue, and palate. In newborns, sucking can
also be elicited by widespread tactile and
acoustic stimuli.
Observations in malformed humans confirm the
existence of a bulbar system for mastication.
The pattern of oral automatisms changes with
aging. Sucking appears first and is replaced by
chewing. Eventually, all oral movements are
voluntarily controlled. Stimulus-sensitive oral
automatisms occur in normal newborns but cannot
be seen in adults except under pathologic
conditions.
The LIS seems to be another pathologic
condition leading to involuntary stimulus evoked
oral automatisms. As in newborns the oral and
perioral region is the most sensitive region but
other regions are also susceptible. Regarding
the ventral part of the pons as the most common
localization of lesions leading to an LIS, one
cannot rule out extrapyramidal mechanisms.
However, according to the observations in
malformations, the most probable explanation for
oral motor phenomena in LIS is the loss of
pyramidal control over the bulbar system for
mastication.
