A 36-year-old woman comes to the emergency department due to left-sided facial droop. The patient woke up 4 hours ago and noticed that the left side of her face was sagging and that she was drooling from a corner of the mouth. She has had no facial numbness but has noticed an increased sensitivity to noise. The patient has a history of migraines, seasonal allergies, and gestational diabetes. Temperature is 36.5 C (97.7 F), blood pressure is 120/70 mm Hg, and pulse is 78/min. BMI is 32 kg/m². The face appears asymmetric with loss of the left nasolabial fold. When the patient is asked to smile, the left side of her face does not move. She is unable to raise her left eyebrow or completely close her left eye. Facial sensation to touch and pain is normal bilaterally. There are no skin or mucous membrane lesions. Which of the following is the most likely cause of this patient's current condition?

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11ec25c8_d552_c158_bc81_cb33ad1a5f69_MD0003_00 This patient likely has Bell palsy, a peripheral neuropathy involving cranial nerve (CN) VII (facial nerve). Characteristic features include unilateral mouth drooping, disappearance of the nasolabial fold, and, importantly, involvement of the upper face (eg, weakness in closing the eye or raising the eyebrow). Upper face involvement distinguishes Bell palsy from upper motor neuron disorders (eg, stroke), which spare the upper face. Other common symptoms of Bell palsy include decreased ipsilateral eye lacrimation, hyperacusis, and decreased sensation of taste over the anterior two-thirds of the ipsilateral tongue. The weakness typically develops acutely over a course of hours; however, it often occurs at night, and patients may awaken with significant facial droop. Symptoms typically progress over 2-3 weeks, with gradual improvement over the following 3-6 months. Bell palsy is thought to be due to reactivation of a neurotrophic virus, most commonly herpes simplex virus. Viral infection causes inflammation and edema of the facial nerve, resulting in nerve compression and degeneration of the myelin sheath. Treatment involves glucocorticoids; because of the association with herpes simplex virus, some experts also recommend the addition of valacyclovir. (Choice A) Migraine with aura involving the brainstem (basilar migraine) manifests with vertigo, dysarthria, diplopia, and possibly loss of consciousness, typically followed by a severe occipital headache. Facial weakness would be unexpected. (Choice B) The corticobulbar tract carries input from upper motor nuclei and innervates CN V, VII, IX, X, XI, and XII. Most of these CNs receive bilateral cortical input and are unaffected by a unilateral lesion (ie, stroke). However, the neurons of CN XII that innervate the genioglossus muscle (tongue) and the neurons of CN VII that innervate the lower face only receive unilateral input. Therefore, stroke involving the corticobulbar tract results in lower facial weakness with sparing of the forehead (due to bilateral innervation of the upper forehead) and tongue deviation. bilateral innervation (Choice C) Microvascular ischemia of a cranial nerve is usually seen in patients with uncontrolled diabetes (diabetic mononeuropathy) or hypertension. Although it can cause a facial nerve palsy similar to Bell palsy, it is highly unlikely in this patient without comorbid diabetes or hypertension. (Choice E) Multiple sclerosis causes patchy demyelination; however, suprapontine lesions in the white matter would result in an upper motor neuron lesion. Patients would have lower facial weakness but the forehead would be spared. Educational objective: Bell palsy is a peripheral neuropathy of the facial nerve (cranial nerve VII) characterized by facial weakness that involves both the upper and lower face. It is thought to be caused by reactivation of neurotrophic viruses (eg, herpes simplex virus), resulting in inflammation, edema, and degeneration of the myelin sheath.

A 36-Year-Old Woman Comes to the Emergency Department Due to Left-Sided