A65-year-old male smoker with a history of
hypertension and hyperlipidemia, presented
within 3 hours of onset of left-sided
hemiplegia, dysarthria, facial droop, and
hemiataxia. His National Institutes of Health
Stroke Scale score was 7, and a non contrast
computed tomography of his brain was normal. He
was treated with intravenous r-tPA (recombinant
tissue-type plasminogen activator) 3.5 hours
from onset. Multiphasic computed tomography
angiography did not reveal any large vessel
occlusion. Despite treatment, his hemiplegia
worsened, resulting in a 2 point increase in
National Institutes of Health Stroke Scale 2
hours post-r-tPA administration.
Magnetic resonance imaging confirmed an
acute infarct in the right corona radiata and
internal capsule without hemorrhagic conversion.
The stroke work-up was significant for LDL-C
(low-density lipoprotein cho- lesterol) of 162
mg/dL, hemoglobin A1c of 5.8%, and unremarkable
echocardiography and telemetry.
Fourteen hours post-r-tPA, the patient
reported that he was able to lift his left
paretic arm off the bed, but only when yawning.
He demonstrated this by simulating a yawn, which
resulted in antigravity left shoulder abduction.
The simulated yawn generated a smaller amplitude
upper limb movement compared with an involuntary
one (Video S1), and he had no control over the
direction and amplitude of the movement. The arm
returned to its original position on the bed at
the end of each yawn. There were no associated
lower limb movements during these episodes.
He received dual antiplatelet therapy and a
course of rehabilitation, with improved National
Institutes of Health Stroke Scale of 3 at 3
months. Power had improved to 3+ in the left
upper limb and 4+ in the left lower limb. The
involuntary movement in his left arm with
yawning gradually disappeared with recovery of
motor power.
DISCUSSION
The involuntary antigravity movement of an
otherwise plegic arm during yawning has been
described in case reports as early as 1844, and
the term parakinesia brachialis oscitans (PBO)
was first coined by Walusinski.1
Described in both the flaccid and spastic
phases of poststroke recovery, the onset of PBO
is variable and can occur fromwithin1 day of the
infarct to as late as 4 monthsafter.2 The
majority of cases report shoulder abduction
occurs exclusively at the onset of a yawn. The
arm then returns to a resting position as the
yawn subsides.1,3 While PBO usually involves the
upper extremity, lower extremity movements have
also been described.3,4 Furthermore, PBO can be
unpleasant as some patients find it distressing
as it can give them a false sense of hope.5
PBO is thought to be a form of parakinesia
as there appears to be an automatic-voluntary
dissociation, whereby voluntary movement of the
paretic limb is not possible but can be
triggered by yawning, an automatic activity.
Another classic example of automatic-voluntary
dissociation is the Foix-Chavany-Marie syndrome,
where biopercular lesions lead to the loss of
voluntary movements of the facial, pharyngeal,
lingual, and masticatory muscles. However,
movements in these muscles can be triggered by
emotions through the activation of alternative
pathways from the amygdala and lateral
hypothalamus to
Although various articles have proposed
different mechanisms for this phenomenon, the
prerequisite condition for PBO seems to be
consistent, it requires an interruption of the
corticospinal and corticopontocerebellar
pathways, and the preservation of
spinocerebellar pathways. Interruption of the
corticopontocerebellar pathway allows the
release of subcortical structures from cortical
inhibition, while preservation of
spinocerebellar pathways allow phylogenetically
primitive structures to modulate movement in
response to yawning. Most commonly, the lesion
responsible for PBO is found at the level of
corticopontine pathway where it passes through
the internal capsule. Distal cortical lesions
without the involvement of the corticopontine
pathway do not cause PBO as there is no
interruption of cortical modulating inhibitory
influence on the cerebellum and spinal motor
neurons.1
Two Main Theories Have Been Proposed for
the Pathophysiology of PBO
1. Emotional motorsystem: A distinct set of
descending fiber tracts within the brain stem
separate from the pyramidal tracts, is proposed
to facilitate an integrated discharge of the
bulbar reticular formation in response to an
emotional state. In this theory, yawning is
thought to represent a somatic manifestation of
a disinterested emotional state. During a yawn,
there is co-activation of bulbar and motor
neurons in the brain stem, resulting in
stretching movements in the upper limb via
intact reticulospinal tracts.6
2. Proprioceptive loop theory: The theory
proposes that the strong contraction of
respiratory muscles during a yawn sends a
proprioceptive signal antidromically to the
anterior spinal horn, cerebellum, and finally
the lateral reticular nucleus in the medulla via
the ventral spinocerebellar tract. A motor
signal from the lateral reticular nucleus is
then formulated in response and travels through
the extrapyramidal pathways of the cerebellum,
back to the anterior horn cell from C4 to C8,
resulting in the involuntary movement of the
paralyzed upper limb. In this case, yawning is
thought to be an exteriorization of a
homeostatic arousal mechanism and is frequently
observed poststroke. A limitation of this theory
is that it does not explain the lower limb
movements observed in some case reports.1 Our
patient_s ability to trigger the involuntary
movement in his plegic arm with a simulated yawn
supports the proprioceptive loop theory.
PBO has been observed in both ischemic and
hemorrhagic infarcts, and in other nonvascular
neurological
conditions like the bulbar form of
amyotrophic lateral sclerosis and brain stem
tuberculoma.2 Clinically, this phenomenon is not
uncommon, occurring in up to 78.6% of anterior
circulation strokes.4 While there are several
case reports of PBO in posterior circulation
infarcts in the literature,2 it is unclear why
it is less commonly reported in infarcts in this
territory. A plausible explanation is that
spinocerebellar pathways are often disrupted in
these cases and, therefore, the prerequisite
conditions for PBO are not met. The large muscle
bulk in the lower limbs may account for less
frequent involvement in PBO.4
The neurophysiology of yawning is not well
understood. It is a stereotyped phenomenon,
observed in both mammalian and nonmammalian
animals and is sometimes accompanied by
elevation of the arms (pan- diculation). The
hypothalamic paraventricular nucleus controls
the lower motor centers in the brain stem that
are involved in yawning, and stimulation of its
oxytocin neurons by dopamine or its agonists
(eg, apomorphine injections) triggers yawning
and erection.7
Excessive yawning poststroke is a
well-recognized clinical sign&emdash;it may
herald brain stem ischemia with dener- vation
hypersensitivity of a putative brain stem yawn
center in posterior circulation infarcts,8 and
in anterior circulation infarcts with insula and
caudate nucleus lesions, the severity of yawning
correlates with clinical (National Institutes of
Health Stroke Scale) and radiological (apparent
diffusion coefficient values) markers of stroke
severity.9 A hypothesis that yawning switches
the default-mode network to the attentional
network by activating cerebrospinal fluid flow
and clearing somnogens from the brain and
reducing sleepiness has been proposed as part of
the aforementioned homeostatic arousal
mechanism.10
Current studies suggest that the increased
brain stem monoaminergic activation associated
with yawning permits movements that are
otherwise absent in those with corticospinal
tract lesions8; however, the use of dopaminergic
medications has not proven effective in motor
rehabilitation poststroke. It does raise the
possibility that in patients with intact
spinoreticulocerebellar pathways (of which PBO
may be a clinical indictor of), the use of
dopaminergic agents may aid in motor
rehabilitation. A previous study did not
identify a prognostic value for PBO in recovery;
although 32/40 stroke patients had PBO, and only
2 attained useful hand function while 25%
remainedplegic.6
In this case report, we present a case of
post ischemic stroke PBO, with a patient who was
able to trigger involuntary movements in an
otherwise plegic arm by simulating a yawn. This
provides further evidence for the proprioceptive
loop theory to explain the pathophysiology
behind this unique condition. We propose that
fur- ther studies can be done to investigate how
to fully use the potential of this neurological
pathway to initiate early rehabilitation for
patients poststroke, and evaluate the clinical
outcomes of patients who exhibit this
phenomenon. Finally, neurologists should be
familiar with involuntary movements that can
occur after a stroke, so as to not mistake them
for abnormal movement disorders and subject
patients to unnecessary investigations.
• Movement of the paretic arm with
yawning poststroke can occur in patients with
lesions along the pyramidal tract (most commonly
in the internal capsule or the pons). It should
not be mistaken for an abnormal movement
disorder.
•PBO is an example of an
autonomic-voluntary dissociation. The loss of
cortical inhibition of the cerebellum
via the corticopontocerebellar pathway,
while the spinoarcheocerebellar pathway remains
functional, explains the phenomenon.
• This phenomenon fades as the patient
progresses in their motor recovery.
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