42-year-old (female) with facial asymmetry

00:03 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.

00:12 She noticed it yesterday but did not seek medical care.

00:16 She denies any trauma to her face or recent travel.

00:20 Her past medical history is noncontributory, Her vital signs include blood pressure 110/78, temperature of 36.5, pulse 78, respiratory rate 11.

00:32 On physical examination, there is drooping of the left side of her face.

00:36 The left nasolabial fold is absent and she is unable to close her left eye or raise the left side of her forehead.

00:43 No additional findings such as a rash or vesicles were noted on her face, ear or oral cavity.

00:49 The rest of the neurological examination is within normal limits.

00:53 When the patient is asked to smile, assymetry is appreciated in the photograph.

00:59 A CT scan of the head is obtained which is normal.

01:02 Which of the following is the most likely cause of her presentation? Answer choice (A) - Varicella-zoster infection Answer choice (B) - Lyme disease Answer choice (C) - Idiopathic Answer choice (D) - cerebrovascular accident or Answer choice (E) - Malignancy Now take a moment to come to your own conclusion before we go over it together.

01:28 Okay let's tackle this question together.

01:30 Now this question is a neurology question in which we have have a patient with a cranial nerve or a nerve lesion.

01:36 And we are asked to localize a lesion and find the underlying cause of the diagnosis.

01:41 Now this is a 2-step question because we have to diagnose to determine the cause.

01:45 And the stem is required to be able to determine physical examination findings and also history of the patient.

01:52 Now let's walk through this question together.

01:54 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.

02:02 Now the signs that we see in this clinical vignette are associated with the facial nerve palsy.

02:09 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.

02:18 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.

02:28 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.

02:40 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.

02:51 Now with the upper motor neuron lesion, we see forehead sparing.

02:55 And the rationale there is that upper motor neurons are bilaterally innervated.

03:00 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.

03:09 So the forehead is duly innervated by the upper motor neurons but the lower face is not.

03:14 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.

03:33 Now this image shows us the difference between the upper motor neuron and lower motor neuron lesion.

03:39 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.

04:07 Now in peripheral lesions - lower motor neuron lesions, the patient cannot move any of these lesions since the entire face will be affected.

04:15 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.

04:25 So now we've localized the lesion, it is a left-sided lower motor neuron facial nerve lesion.

04:31 Now we've identified the cause of this facial nerve palsy.

04:36 Now, lower motor neuron facial nerve palsies can occur from skull fractures or injury to the face.

04:42 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.

04:52 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.

05:10 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.

05:20 And also here we made the comment that middle ear damage can be seen following a varicella-zoster infection.

05:26 You can look in the patient's ear and look for vesicles.

05:29 If you do, you should be suspecting a condition known as Ramsay-Hunt disease.

05:33 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.

05:51 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'.

06:05 Thus the correct answer in this case is answer choice (C) - idiopathic facial nerve palsy also called Bell's palsy.

06:13 Now let's review some high-yield facts regarding the facial nerve palsy and the causes of facial nerve palsies.

06:20 Now facial nerve paralysis is characterized by unilateral facial weakness.

06:26 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.

06:36 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.

06:47 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.

06:54 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.

07:02 You can also have decreased salivation and tearing as that can also be caused due to the cranial nerve VII innervation.

07:09 Other symptom we should include is hyperacusis, which is the increased sensitivity to sounds.

07:14 This is caused by the denervation of the stapedius muscle.

07:18 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.

07:30 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.

07:42 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.

08:12 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.

08:33 Now the most lower neuron facial palsies have no cause and are termed idiopathic and are often called Bell's palsy.

08:41 A little bit of a hint and a guide into step 2 and step 3 management, Bell's palsy is idiopathic.

08:47 they are treated within the first 3 days, you can give antiretrovirals or steroids.

08:52 however after 3 days, we do not treat and it should self-resolve over time.