Yawning is sociobiological stereotyped
behaviour exhibiting an active involuntary deep
inspiraion involving the mimic muscles. It
probably represents an arousal defence reflex
occurring at moments of increased vulnerability
such as drowsiness (Askenasy
1989).
Pathophysiology an anatomical site are badly
understood. In man the striatum, hypothalamus
and brainstem have been implicated (Gschwend
1977; Sandyk
1987; Winalaratama
1988). Yawning may occur in physiological and
pathological conditions (Blin
1991).
Excessive yawning as an isolated sign may
represent a major diagnostic problem.
A 40 year old woman was refred for excessive
continuous yawning with regular 1 Hz pattern and
acute onset. She had received clonazepam,
phenytoin, amitriptylin,
procyclidinehydrochloride and flunarizine
without sustained benefit. Neurological and CT
investigations were normal. PSG-screening showed
no signs of dys- or hypersomnia : two
consecutive sleeprecordings showed a high sleep
efficiency (94 &96%), normal REM latency
(105 min.) and relative low SWS and REM
percentages (8 & 15%). Respiration was
regular, MSLT showed no increased sleep
pressure. The patient took no drugs, except for
estrogens.
In fact 7 days before symptom onset she had
switched to a new hormonal preparation. She took
2 mg oestradiol combined with 1 mg
cyproteronacetate (Climen) in a cyclical daily
regimen. She had received gonadotropin (Humegon)
and anti-estrogen (Clomid) treatments before.
Ten days following estrogen withdrawal all
symptoms had disappeared.
Recent neuropharmacological research favours
the involvement of dopaminergic mechanisms, in
yawning (Lal et
al., 1987). This also opens the possibility of a
hormonal modulation. Estrogens may induce chorea
in patients with preexisting abnormalities of
the basal ganglia showing altered central
dopaminergic activity (Nausieda et al., 1986).
However the effect of estrogens depends on the
dose, the time interval, the type of behaviour
measured and the part of the basal ganglia
involved (Van Hartesveldt and Joyce, 1986). This
partly explains the controversial data
regarding, estrogen induced DA-receptor hyper-
or hyposensitivity. Experimental results suggest
a pathogenetic hyposensitivity of DA
autoreceptors (Piccardi et al 1983). Apomorphine
stimulates DA autoreceptors and induces yawning,
in both animals and man (Lal
et al., 1987). In animals it is a
predominantly male phenomenon, but human
observations suggest an eventual species and
gender difference. Although other neurochernical
disturbances have been implicated (Blin
et al., 1991) this observation may sharpen
our attention to hormonal status and gender
effects in patients complaining of excessive
yawning.
