A 42 year old woman presents to her physician
with the complaint of facial assymetry
as her face appears to be
deviated to the right.
She noticed it yesterday but
did not seek medical care.
She denies any trauma to
her face or recent travel.
Her past medical history is noncontributory,
Her vital signs include blood pressure 110/78,
temperature of 36.5, pulse 78, respiratory rate 11.
On physical examination, there is
drooping of the left side of her face.
The left nasolabial fold is absent and she is unable to
close her left eye or raise the left side of her forehead.
No additional findings such as a rash or vesicles
were noted on her face, ear or oral cavity.
The rest of the neurological
examination is within normal limits.
When the patient is asked to smile,
assymetry is appreciated in the photograph.
A CT scan of the head is
obtained which is normal.
Which of the following is the most
likely cause of her presentation?
Answer choice (A) -
Answer choice (B) - Lyme disease
Answer choice (C) - Idiopathic
Answer choice (D) -
or Answer choice (E) - Malignancy
Now take a moment to come to your own
conclusion before we go over it together.
Okay let's tackle this question together.
Now this question is a neurology question in which we
have have a patient with a cranial nerve or a nerve lesion.
And we are asked to localize a lesion and
find the underlying cause of the diagnosis.
Now this is a 2-step question because we have
to diagnose to determine the cause.
And the stem is required to be able to determine physical
examination findings and also history of the patient.
Now let's walk through
this question together.
The first thing we need to do is
identify which nerve is affected,
or as we say in neurology, we need
to first localize the lesion.
Now the signs that we see in this clinical vignette
are associated with the facial nerve palsy.
Now recall that the facial nerve controls
some muscles of facial expression
but also controls taste sensation
for the anterior 2/3 of the tongue.
Now the facial nerve can have a lesion that is
either central, which we call a supranuclear lesion,
or peripheral and then we can facial
nerve involvement from either site.
Now let's look at the image to help us
better understand facial nerve lesions
whether at the upper motor neuron nuclear
level or at the lower motor neuron nerve level.
Now as we can see on the image, we have a
lower motor neuron palsy seen on the left
in which we have a full facial droop involving
the lower face but also the forehead.
Now with the upper motor neuron
lesion, we see forehead sparing.
And the rationale there is that upper
motor neurons are bilaterally innervated.
So if I cause a lesion to one
of the upper motor neurons,
the other upper motor neuron can also
take over and protect the forehead.
So the forehead is duly innervated by the upper
motor neurons but the lower face is not.
Now as we can see with lower motor neuron, the entire
forehead and face no longer has innervation and movement,
thus we have full facial droop and with upper
motor neuron, we have forehead sparing
due to the upper motor neuron bilateral
innervation of the forehead,
very high yield to
understand this difference.
Now this image shows us the difference between the
upper motor neuron and lower motor neuron lesion.
Now what we can see is that in patients and again to kind of
highlight because this is extremely important to understand
both for USMLE exams and also being on the wards,
that when you have an upper motor neuron lesion,
the forehead and the ability to close
the eyes is maintained as though
we have bilateral upper motor
neuron lesion to the upper face
which includes the closure of the
eyelids and also the forehead.
Now in peripheral lesions -
lower motor neuron lesions,
the patient cannot move any of these lesions
since the entire face will be affected.
As in this case, the patient is unable to
close her left eye or raise the left forehead
and she does have a peripheral lesion or
what is called a lower motor neuron lesion.
So now we've localized the lesion, it is a
left-sided lower motor neuron facial nerve lesion.
Now we've identified the cause
of this facial nerve palsy.
Now, lower motor neuron facial nerve palsies can
occur from skull fractures or injury to the face.
You can also have a head or neck
tumor that can cause this lesion
or you can ave middle ear damage such as
following a varicella-zoster infection.
Now you can also have direct nerve
damage as in the case of Lyme disease,
however the case of Lyme disease,very important
to know is traditionally going to have a
bilateral lower motor neuron facial nerve
palsy, so wouldn't be just one sided.
That's not to say that all Lyme disease
always produces bilateral lesions,
but for the sake of the USMLE exam, if you see
bilateral, you should be thinking Lyme disease.
And also here we made the comment that middle ear damage
can be seen following a varicella-zoster infection.
You can look in the patient's
ear and look for vesicles.
If you do, you should be suspecting a
condition known as Ramsay-Hunt disease.
Now in this patient, we don't see any
trauma, we don't see any history of cancer,
we don't see any middle ear damage on examination,
and there is no recent travel or a skin comment
to can make us think of Lyme disease nor
is there any bilateral facial nerve palsy.
Thus in the absence of any history or sign
to tell us any of these underlying cause,
the most likely cause for this
patient is an idiopathic cause
and this idiopathic facial nerve palsy
is commonly called 'Bell's palsy'.
Thus the correct answer in this case is answer choice (C)
- idiopathic facial nerve palsy also called Bell's palsy.
Now let's review some high-yield facts regarding the
facial nerve palsy and the causes of facial nerve palsies.
Now facial nerve paralysis is characterized
by unilateral facial weakness.
But what you can also have is loss of
taste in the anerior 2/3 of the tongue
and the way to test that is to take a
q-tip and dip it in a very salty water.
Have the patient protrude their tongue, touch
one side of the tongue and then the other
and without them putting the tongue back in the mouth,
ask them which side do they feel less salt sensation.
And the reason why you don't want them
to put their tongue back in their mouth
is that the saliva will cause mixing
all over and it will ruin the exam.
So just dab each side of the anterior 2/3 of the tongue
and then ask the patient where there is decreased side
and that shall support the lesion to
that side of the cranial nerve VII.
You can also have decreased salivation
and tearing as that can also be caused
due to the cranial nerve VII innervation and you can also have
decreased hearing as decreased innervation to the stapedius.
Now for lower motor neuron palsies, the
upper part of the face is also affected
such that the patient cannot close
their eye or raise their forehead
as the muscles in that case
are not duly innervated.
Now in an upper motor neuron, the upper face is spared
due to the upper motor neuron bilateral innervation
of both the forehead
and eye closure.
Now you will commonly see loss of left or right
depending on what side, nasolabial fold flattening
in the patient with facial weakness, that's
a very characteristic way to identify
Now the causes of facial nerve palsy, the main cause of an
upper motor neuron facial nerve palsy is due to a stroke
or also what's called a cerebrovascular
accident, and this will result
in lower facial weakness contralateral
to neurological lesion.
Now lower motor neuron facial palsies may
be due to a trauma of the skull base,
head and neck tumors, middle ear damage
following a varicella-zoster infection
in which you will see vesicles in the
ear also called Ramsay-Hunt Syndrome,
or from direct nerve damage seen in Lyme disease
which can produce a bilateral facial nerve palsy.
Now the most lower neuron facial palsies have no cause
and are termed idiopathic and are often called Bell's palsy.
A little bit of a hint and a guide into step 2 and
step 3 management, Bell's palsy is idiopathic.
they are treated within the first 3 days,
you can give antiretrovirals or steroids.
however after 3 days, we do not treat
and it should self-resolve over time.