Bell palsy — Transcript

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1. 0:02Bell's palsy, named after the Scottish
2. 0:04doctor Charles Bell, who first described
3. 0:07the condition, is the most common type
4. 0:09of facial nerve palsy.
5. 0:11Facial palsy occurs when there's damage
6. 0:13to the facial nerve, also known as the
7. 0:15seventh cranial nerve, which results in
8. 0:17weakness and paralysis on one side of
9. 0:19the face.
10. 0:20This can happen due to various
11. 0:22conditions, including stroke or tumors,
12. 0:24but if the underlying cause remains
13. 0:26unknown, we call it Bell's palsy.
14. 0:28Remember when you were a kid and felt
15. 0:30crushed because your family was watching
16. 0:32a movie instead of your favorite
17. 0:33cartoon? That grumpy face you made,
18. 0:36that's your facial nerve telling your
19. 0:37muscles what to do.
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26. 0:55>> The ultimate control of facial muscles
27. 0:57comes from the left and right upper
28. 0:59motor neurons in the primary motor
29. 1:01cortex of the precentral gyrus.
30. 1:05First, let's talk about the lower right
31. 1:07half of the face. The upper motor neuron
32. 1:09from the left side of the brain travels
33. 1:11down to the brainstem, crosses over the
34. 1:13midline, and connects to a lower motor
35. 1:16neuron in the facial nucleus.
36. 1:18From here, the lower motor neuron sends
37. 1:20signals through the right facial nerve
38. 1:22to the lower right half of the face.
39. 1:24So, when it comes to the lower part of
40. 1:26your face, each side of your brain
41. 1:28handles the opposite lower side.
42. 1:31But, the upper half of the face is like,
43. 1:33"Nah, I want to back up and signals from
44. 1:35both sides of the brain."
45. 1:37In this case, the upper motor neuron
46. 1:39from the left side of the brain extends
47. 1:40to the lower motor neuron on the
48. 1:42opposite side.
49. 1:43But, at the same time, the upper motor
50. 1:45neuron from the right side sends back up
51. 1:48to the lower motor neuron on that same
52. 1:49side.
53. 1:50So, when it comes to the upper half of
54. 1:52the face, both sides of your brain team
55. 1:54up to get the job done.
56. 1:58Now, let's focus on the facial nerve,
57. 2:00which emerges from the pontomedullary
58. 2:02junction of the brainstem. Next, it
59. 2:04enters the petrous part of the temporal
60. 2:06bone, where it travels through a narrow
61. 2:08Z-shaped canal called the facial canal.
62. 2:11After passing through the canal, it
63. 2:12exits the skull through a small opening
64. 2:14in the temporal bone called the
65. 2:16stylomastoid foramen.
66. 2:18From here, the facial nerve passes
67. 2:20through the parotid gland, where it
68. 2:21branches off to innervate various facial
69. 2:24muscles, which are responsible for
70. 2:25facial expressions.
71. 2:28The facial nerve also controls the
72. 2:30submandibular and sublingual glands,
73. 2:32which produce saliva, as well as the
74. 2:34lacrimal gland, which creates tears.
75. 2:37It also carries taste sensations from
76. 2:39the front 2/3 of your tongue and
77. 2:41innervates the stapedius muscle, which
78. 2:43helps reduce the vibrations of the
79. 2:44stapes bone against the oval window,
80. 2:47protecting your hearing from loud
81. 2:48noises.
82. 2:50Now, Bell's palsy is also known as
83. 2:52idiopathic facial nerve palsy because
84. 2:55the underlying cause is unknown.
85. 2:57However, we know that it involves
86. 2:59inflammation of the nerve within the
87. 3:00facial canal.
88. 3:02As the nerve becomes inflamed and
89. 3:03swells, it has little room to expand.
90. 3:06This increases pressure on the small
91. 3:08blood vessels supplying the nerve,
92. 3:10eventually reducing blood flow and
93. 3:12causing nerve ischemia and dysfunction.
94. 3:15And since small blood vessels are
95. 3:16crucial in nourishing the nerve,
96. 3:18remember that conditions affecting small
97. 3:20blood vessels, like uncontrolled
98. 3:21diabetes and hypertension, can increase
99. 3:24the risk of developing Bell's palsy.
100. 3:27In some individuals, herpes simplex
101. 3:29virus type 1 can reactivate from its
102. 3:31dormant state in the geniculate ganglion
103. 3:33and travel along the facial nerve,
104. 3:35leading to inflammation.
105. 3:37This helps explain why this virus is
106. 3:39often found in the endoneurial fluid
107. 3:41around the affected nerve.
108. 3:44Now, in Bell's palsy, signals from both
109. 3:46upper motor neurons are still reaching
110. 3:48lower motor neurons.
111. 3:50But on the affected side, as the signal
112. 3:52travels along the facial nerve through
113. 3:54the facial canal, it gets blocked.
114. 3:56In other words, it never reaches facial
115. 3:59muscles, causing complete weakness in
116. 4:01both the lower and upper halves of the
117. 4:02face.
118. 4:04When the lower part loses innervation,
119. 4:06the corner of the mouth droops, which
120. 4:08can lead to drooling.
121. 4:10If the person smiles, the smile looks
122. 4:11uneven, and the skin fold running from
123. 4:13the side of the nose to the corner of
124. 4:15the mouth disappears. This is called the
125. 4:17loss of the nasolabial fold.
126. 4:20Finally, puffing out the cheeks is
127. 4:22almost impossible, so simple things like
128. 4:24blowing up a balloon for a birthday
129. 4:25party become a real struggle.
130. 4:28On the flip side, when the upper half
131. 4:30loses innervation, the forehead on that
132. 4:32side loses its wrinkles, and the person
133. 4:34cannot raise their eyebrow.
134. 4:36The muscles around the eye become weak,
135. 4:38making it difficult to fully close the
136. 4:40eye. When they try, the eye moves
137. 4:42upward, which is known as the Bell
138. 4:44phenomenon.
139. 4:45And since they can't blink properly, the
140. 4:47eye doesn't get the moisture it needs,
141. 4:49which can lead to dryness and even
142. 4:51corneal ulcers.
143. 4:54And the story doesn't end with just
144. 4:55muscle weakness.
145. 4:57Since the facial nerve also controls the
146. 4:59submandibular and sublingual glands,
147. 5:01individuals with Bell's palsy may
148. 5:03experience a dry mouth.
149. 5:05On top of that, losing sensation from
150. 5:07the front two thirds of the tongue means
151. 5:09no taste of their favorite vanilla ice
152. 5:11cream.
153. 5:12And finally, when the stapedius muscle
154. 5:14stops working properly, everyday sounds
155. 5:16that usually feel fine can suddenly seem
156. 5:18unbearably loud. This is known as
157. 5:21hyperacusis.
158. 5:22Keep in mind that all these symptoms
159. 5:24often start with pain around the ear and
160. 5:26usually develop quickly, often within
161. 5:28just a few hours.
162. 5:31Now, to diagnose Bell's palsy, the first
163. 5:33step is to rule out central causes of
164. 5:35facial palsy. The main clue is the
165. 5:37forehead.
166. 5:38If a person can still wrinkle the
167. 5:40forehead on the weak side, it's likely
168. 5:42central facial palsy.
169. 5:44For example, a tumor, stroke, or
170. 5:46multiple sclerosis can affect the upper
171. 5:48motor neuron on one side of the brain,
172. 5:50stopping it from sending signals to the
173. 5:52facial nucleus on the opposite side.
174. 5:55However, the upper motor neuron on the
175. 5:57unaffected side still sends backup
176. 5:59signals to both facial nuclei, including
177. 6:01the one on the affected side of the
178. 6:03face. This allows the forehead muscles
179. 6:05to move.
180. 6:07But, if your patient can't wrinkle the
181. 6:08forehead on the weak side, diagnose
182. 6:10peripheral facial palsy.
183. 6:12In this case, both upper motor neurons
184. 6:14are sending signals to the facial
185. 6:16nuclei, but the signal from the facial
186. 6:18nucleus on the affected side is not
187. 6:20reaching the facial muscles.
188. 6:23Next, rule out potential causes of
189. 6:25peripheral facial palsy.
190. 6:27First, acoustic neuroma is a benign
191. 6:29tumor of Schwann cells of the
192. 6:31vestibulocochlear nerve.
193. 6:33It usually develops in the
194. 6:34pontomedullary angle, close to the
195. 6:36facial nerve. As it grows, it compresses
196. 6:39the facial nerve, causing facial palsy.
197. 6:41On top of weakness, individuals may
198. 6:43experience hearing loss and balance
199. 6:45issues.
200. 6:47Next, mumps infection can trigger
201. 6:49parotitis or inflammation of the parotid
202. 6:51gland.
203. 6:53The swollen gland can press on the
204. 6:54facial nerve as it passes through,
205. 6:56leading to facial palsy.
206. 6:58Finally, Lyme disease, caused by the
207. 7:00bacterium Borrelia burgdorferi, can
208. 7:03result in unilateral or bilateral facial
209. 7:05palsy.
210. 7:07In this case, look for a characteristic
211. 7:09rash called erythema migrans and ask
212. 7:11about possible tick exposure.
213. 7:14Once you rule out all these potential
214. 7:16causes, you can diagnose Bell palsy.
215. 7:20Treatment primarily relies on
216. 7:21corticosteroids to reduce nerve
217. 7:23inflammation and sometimes antiviral
218. 7:25medications to fight the herpes simplex
219. 7:27virus.
220. 7:29All right, as a quick recap, Bell palsy
221. 7:31is also known as idiopathic facial nerve
222. 7:33palsy because the exact cause remains
223. 7:36unknown.
224. 7:37However, we know that it involves
225. 7:39inflammation of the nerve within the
226. 7:40facial canal.
227. 7:42And as the nerve swells, it has little
228. 7:44room to expand, which increases pressure
229. 7:46on the small blood vessels that nourish
230. 7:48it. This pressure reduces blood flow,
231. 7:50causing nerve ischemia and dysfunction.
232. 7:53Common symptoms include an inability to
233. 7:55wrinkle the forehead or close the eye,
234. 7:57loss of the nasolabial fold, and
235. 7:59drooping of the mouth on the affected
236. 8:01side.
237. 8:14>> Helping current and future clinicians
238. 8:16focus, learn, retain, and thrive. Learn
239. 8:19more.