A 65-year-old man with a history of hypertension is brought to the hospital due to sudden-onset vertigo and dizziness that started an hour ago. On physical examination, there is ptosis and pupillary constriction in the left eye. Extraocular movements are normal in both eyes. Pain and temperature sensations are decreased over the left side of the face, and the direct corneal reflex is absent on the left. Pain and temperature are also decreased over the right side of the body. Muscle strength is 5/5 in all 4 extremities with normal deep tendon reflexes. Which of the following is the most likely cause of this patient's asymmetrical pupils?

Question

A 65-year-old man with a history of hypertension is brought to the hospital due to sudden-onset vertigo and dizziness that started an hour ago.  On physical examination, there is ptosis and pupillary constriction in the left eye.  Extraocular movements are normal in both eyes.  Pain and temperature sensations are decreased over the left side of the face, and the direct corneal reflex is absent on the left.  Pain and temperature are also decreased over the right side of the body.  Muscle strength is 5/5 in all 4 extremities with normal deep tendon reflexes.  Which of the following is the most likely cause of this patient's asymmetrical pupils?

Quizplus · Accepted Answer

11ec160b_35ba_f98c_9249_71226ac4291d_MD0001_00 This patient with acute vertigo, sensory loss, and abnormal eye findings most likely suffered a stroke affecting the brainstem. The presence of unilateral ptosis and miosis indicates impaired sympathetic activity (ie, Horner syndrome). Sympathetic innervation of the eye follows a complex pathway: This patient also has a unilateral loss of the direct (afferent) corneal reflex, which is mediated by the ophthalmic nerve (CN V1). In combination with the loss of pain and temperature sensation on the same side of the face, these findings suggest damage to the ipsilateral spinal trigeminal nucleus in the lateral medulla. The patient's vertigo (vestibular nucleus) and contralateral loss of pain and temperature sensation of the body (spinothalamic tract) are further consistent with damage to the lateral medulla (ie, lateral medullary syndrome). (Choice A) Abnormal neuromuscular junction function can result in myasthenia gravis, which often causes asymmetric fluctuating ptosis. However, patients with myasthenia gravis often have diplopia, the pupils are not affected, and they do not have sensation deficits. (Choice B) The oculomotor nerve (CN III) provides parasympathetic input to the iris and lens, and also regulates pupillary constriction. However, damage to parasympathetics would lead to abnormal pupillary dilation. In addition, because CN III provides motor innervation to most of the extraocular muscles, dysfunction would also lead to abnormal extraocular movements. (Choice C) Compression of the trigeminal nerve (CN V) could lead to impaired facial sensation and an absent corneal reflex (due to interruption of the afferent sensory limb of the corneal reflex). However, it would not lead to ptosis or a constricted pupil. (Choice D) A constricted pupil occurs in Horner syndrome because the normal parasympathetic activity is not balanced by the sympathetic activity. This relative overactivity of parasympathetics when compared to the activity of sympathetics leads to pupillary constriction. Decreased parasympathetic activity would be expected to cause a dilated pupil. Educational objective: A stroke in the lateral brainstem can lead to ipsilateral Horner syndrome because sympathetic neurons travel next to the spinothalamic tract in the lateral medulla.

A 65-Year-Old Man with a History of Hypertension Is Brought