Yawning is an arousal reflex to reverse
brain hypoxia [?]. Physiologically
boredom and tiredness induce the involuntary
wide opening of the mouth with massive air
inhalation through mouth and nose followed by
slow expiration. Ancyloglossia, epilepsy,
psychosi, encephalitis and brain tumours are
known causes of yawning as a repetitive
phenomenon. Pharmacologically it can be provoked
by drug overdose with valproate, dopamine
agonists, tricyclic antidepressants or by of
morphine. Owing to the unclear mechanisrn and
borderline position between psychology and
neurology, there has been little medical
research on the phenornenon. We report the case
of a patient with excessive pathological
yawning, hemiparesis and facial paresis as
symptoms of multiple sclerosis (MS). A
28-year-old man had clinically definite MS for 2
years. The patient was admitted to hospital
because of a relapse with mild weakness of the
left extremities. At the same time, yawning
occurred 4 times/min despite regular and
long sleep. Neurological examination showed
central left facial paresis and mild left
spastic hemiparesis. Abdominal reflexes were not
present. Cerebellar function, cranial nerves and
sensory pathways were normal. On T2-weighted
images MRI disclosed multiple lesions of the
brain stem. Visual evoked potentials and brain
stem auditory evoked potentials showed a marked
delay bilaterally. Cerebrospinal fluid revealed
a normal cell count and protein concentration;
oligoclonal bands were positive. A restrictive
or obstructive respiratory tract disease was
excluded using a pulmonary function test.
Arterial blood gas analysis was normal.
Ancyloglossia or deviation of the epiglottis
were not found.
The patient received high-dose intravenous
steroid therapy (methylprednisolone 500 mg for 5
days). On the 3rd day, there was complete
remission of pathological yawning; mild
hemiparesis and facial paresis remitted after 5
days. Although the exact mechanism of yawning is
poorly understood, some trials support the
hypothesis that the ascending activating
reticular system (AARS) and adjoining reticular
neuron complexes can be considered as the
yawning centre. Patients with pons tumours were
able to yawn despite paralysis of the
masticatory muscles. Probably reflex yawning was
possible because of the undisturbed short
interconnections between the reticular neurons
and the motor axons of the fifth and seventh
cranial nerve.
These reports on anatomical aspects of
yawning suggest that an inflammatory affection
of the brain stem in MS patients may also cause
the phenomenon by irritating the AARS. The
discrepancy of the frequently existing brain
stem lesions in MS and the rare incidence of
pathological yawning remains unclear. High-dose
intravenous steroid therapy reverses breakdown
of the blood-brain barrier that is associated
with a loss of gadolinium-enhancing lesions on
MRI. Another cause of favourable short-terin
recovery is the resolution of perifécal
oedema. The rapid clinical response of our
patient with complete remission of the
repetitive phenomenon and hemiparesis may be
explained by these effects, although spontaneous
remission cannot be excluded. Unlike
pathological laughter and weeping, yawning has
not been known to be a pathological phenomenon
in MS. Because of the subjective impairment,
high-dose steroid therapy should be carried out,
even if the phenomenon occurs as a single
symptom.
