A 68-year-old woman comes to the emergency department for evaluation of stroke-like symptoms. The patient says her face appeared "twisted" this morning but was normal when she went to bed last night. Her brother recently had a stroke, and she was worried that she may also be having a stroke. The patient has a history of hypertension, hyperlipidemia, and type 2 diabetes mellitus. Vital signs are within normal limits. Physical examination shows facial asymmetry with drooping of the left corner of the mouth and loss of the left nasolabial fold. Which of the following additional examination findings on the affected side would be most suggestive of central nervous system involvement?
Show Explanatory Sources
Voluntary facial movement is initiated by the motor cortex (located in the frontal lobe), which delivers input to the facial nerve (CN VII), a peripheral nerve that innervates the muscles of facial expression. Central or peripheral lesions can often be distinguished by assessing movement in the upper face.
Central nervous system lesions (eg, stroke) typically affect the motor cortex or the descending tracts; this results in contralateral lower face weakness. However, the nuclei that innervate the upper face receive bilateral input from the motor cortices, so movement of the upper facial muscles (eg, forehead, brow) is often spared.
Peripheral nerve lesions (eg, Bell palsy) affect the entire facial nerve. This results in unilateral weakness of half of the face; forehead movement is lost.
The most common cause of acute unilateral upper and lower facial weakness is Bell palsy, an acute peripheral neuropathy of CN VII. Common findings include an inability to raise the eyebrow or close the eye, drooping of the mouth corner (with the mouth drawn to the unaffected side), and disappearance of the nasolabial fold. For most patients, partial or complete recovery occurs within 3-4 months.
(Choices A, C, and D) Patients with facial nerve lesions often have decreased tear production (due to loss of parasympathetic innervation to the lacrimal gland), hyperacusis (due to weakness of the stapedius muscle), and decreased sensation of taste over the ipsilateral anterior two-thirds of the tongue (which is innervated by the chorda tympani nerve, a branch of the facial nerve).
(Choice B) The platysma muscle, responsible for tensing the skin on the neck, is also innervated by the facial nerve. It would be affected in both central and peripheral lesions.
Educational objective:
Because the upper face receives bilateral input from the motor cortices, central nervous system lesions typically cause lower facial weakness that spares the forehead on one side of the face. In contrast, peripheral lesions (eg, Bell palsy) cause weakness of the entire side of the face. Bell palsy may also result in decreased tear production, hyperacusis, and reduced taste sensation.