Inverse Marcus Gunn phenomenon is a rare
congenital synkinetic movement presenting as
eyelid drooping on jaw opening. It has only
rarely been reported. Often this phenomenon
follows peripheral facial palsy, suggesting
abnormal synkinesis of the facial nerve.
However, the precise mechanism remains
uncertain. Only one electromyographic study has
been reported in this condition. In that case,
trigemino-oculomotor synkinesis was the supposed
mechanism, rather than trigeminofacial
synkinesis. We report a patient with familial
inverse Marcus Gunn phenomenon and speculate on
the neuronal mechanism with the support of
electromyographic results.
A 31 year old woman visited our clinic
complaining of involuntary winking of her left
eyelid on jaw opening. The symptom was most
prominent when she opened her mouth forcefully,
such as when eating or yawning. She
stated that the symptom had been noticed from
birth, and that her mother and uncle were also
affected, but not her two sons. She had no
history of previous peripheral facial
palsy.
On neurological examination, her extraocular
movements were normal and ptosis was not noted.
There was no facial paralysis or sensory
changes. Masticatory movement or forced mouth
opening induced closure of the left eye. Her
mother showed the same feature on neurological
examination. Brain MRI showed no abnormal
findings. Facial nerve conduction studies and
the blink reflex were normal. Two channel
electromyography showed co-contraction of the
left lateral pterygoid muscle and the
orbicularis oculi muscle on repetitive
masticatory movements.
Inverse Marcus Gunn phenomenon, the opposite
of the Marcus Gunn phenomenon, is characterised
by eyelid closure on jaw opening. Few cases have
been reported, most following peripheral facial
paralysis. Only one case of congenital inverse
Marcus Gunn phenomenon was reported by Lubkin.
He observed that on electromyography the levator
palpebrae muscle was inhibited or inactivated
during jaw opening, without any movement of the
orbicularis oculi muscle, and concluded that his
patient's symptom was limited to interactions at
the level of the third and fifth cranial nerve
complexes. Because the Marcus Gunn phenomenon is
a pterygoid-levator synkinesis between the
pterygoid and the levator palpebrae muscles,
Lubkin's case may be the true inverse Marcus
Gunn phenomenon. However, our patient's
electromyographic studies showed that the
ipselateral orbicularis oculi muscle
co-contracted with the lateral pterygoid muscle
when she opened her mouth. Because these
findings were consistently reproducible, we
think this phenomenon is caused by synkinesis of
the trigeminal and facial nerves in our
case.
Most cases of inverse Marcus Gunn phenomenon
appear to follow peripheral facial nerve
paralysis, with contraction of the orbicularis
oculi on jaw opening. However, our patient had
no history of peripheral facial paralysis and
surprisingly her mother and uncle showed the
same phenomenon. We therefore conclude that our
patient has a congenital trigemino-facial
synkinesis with partial autosomal dominant
inheritance. The orbicularis oculi muscle is
supplied by the facial nerve connected to
maxillary and buccal branches of the trigeminal
nerve. As Rana pointed out, ascending
proprioceptive impulses from muscle stretch
during full mouth opening that are carried in
the facial nerve could then trigger contraction
of the orbicularis oculi muscle owing to faulty
regeneration after a traumatic nerve injury.
More recently there has been a tendency to
explain these synkinetic movements in terms of
plastic change in the central nervous system
following deafferentiation. As our patient's
symptom is congenital, we suppose that the
trigemino-facial synkinesis is the result of an
abnormal partial connection between the motor
neurones of the trigeminal and facial
nerves,
References
DeJong RN. The neurologic examination, 5th t
ed. Philadelphia: Lippincott, 1992:178.
Lubkin
V. The inverse Marcus Gunn phenomenon. An
electromyographic contribution. Arch Neurol
1978;35:249.
Marin Amat M Sur le syndrome ou
phénomène de Macus Gunn Annales
d'occulistique Paris 1919; 156; 513-528
Pavesi
G, Medici D, Macaluso G, et al Unsual
synkinetic movements between facial muscles and
respiration in hemifacial spasm Mov Disord.
1994; 9; 4; 451-454
