A 64-year-old woman is brought to the emergency department due to sudden-onset double vision for the past few hours. She has had no headache, vertigo, or slurring of speech and no focal weakness or numbness. The patient has a history of hypertension, type 2 diabetes mellitus with poor glycemic control, and chronic kidney disease. She smokes cigarettes but does not use alcohol or illicit drugs. Blood pressure is 140/90 mm Hg and pulse is 82/min. Physical examination shows ptosis of her right eye. The right eyelid is manually elevated, showing the right eye in a "down-and-out" position. Right eye adduction, elevation, and depression movements are significantly impaired. Left extraocular movements are normal in all directions. Bilateral pupils are equal and reactive to light. The remainder of the neurologic examination is normal. Which of the following is the most likely cause of this patient's current condition?

Question

A 64-year-old woman is brought to the emergency department due to sudden-onset double vision for the past few hours.  She has had no headache, vertigo, or slurring of speech and no focal weakness or numbness.  The patient has a history of hypertension, type 2 diabetes mellitus with poor glycemic control, and chronic kidney disease.  She smokes cigarettes but does not use alcohol or illicit drugs.  Blood pressure is 140/90 mm Hg and pulse is 82/min.  Physical examination shows ptosis of her right eye.  The right eyelid is manually elevated, showing the right eye in a "down-and-out" position.  Right eye adduction, elevation, and depression movements are significantly impaired.  Left extraocular movements are normal in all directions.  Bilateral pupils are equal and reactive to light.  The remainder of the neurologic examination is normal.  Which of the following is the most likely cause of this patient's current condition?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d555_a78c_bc81_f5bfb78b651a_MD0003_00 This patient has clinical findings suggestive of oculomotor nerve (CN III) palsy. The most common cause of CN III palsy in adults is ischemic neuropathy due to poorly controlled diabetes mellitus. CN III has 2 major components as follows: Inner somatic fibers - innervate the levator muscle of the eyelid and 4 of the extraocular muscles (EOMs) (superior rectus, medial rectus, inferior rectus, inferior oblique) Superficial parasympathetic fibers - innervate the sphincter of the iris and the ciliary muscles (controlling pupil constriction). Because the inner somatic fibers are farther from the blood supply, they are more susceptible to ischemic injury. Therefore, patients with ischemic CN III palsy typically have paralysis of the levator muscle (ptosis) and 4 EOMs ("down-and-out-gaze") with preserved pupillary response. (Choices A and B) A midbrain demyelinating lesion or lacunar infarction can damage the CN III nuclei, resulting in deficits to both the somatic and parasympathetic fibers (the pupil is usually affected). These lesions are almost always associated with other neurologic deficits (eg, cerebellar ataxia, hemiparesis). (Choice C) EOM infiltration (eg, inflammatory, neoplastic, infective) can result in unilateral or bilateral ophthalmoparesis, which typically does not isolate to a single cranial nerve. This patient with vascular risk factors has deficits isolated to CN III, suggesting an ischemic etiology. (Choice D) Myoneural junction disorders (eg, myasthenia gravis) are usually characterized by fluctuating, fatigable EOM abnormalities that do not isolate to a single cranial nerve. (Choice E) Nerve compression (eg, aneurysm, tumor) of CN III can cause similar manifestations to ischemic palsy. However, nerve compression usually also affects the parasympathetic fibers, leading to an abnormal pupillary response (eg, mydriasis). (Choice F) Isolated nerve inflammation (eg, vasculitis, autoimmune disorders) of CN III is much less common than an ischemic pathology, especially in patients with extensive vascular risk factors. Educational objective: Ischemic oculomotor (CN III) palsy is commonly associated with poorly controlled diabetes mellitus and is characterized by damage to the inner somatic nerve fibers while sparing the more peripheral parasympathetic fibers. This manifests with ptosis, "down-and-out" gaze, diplopia, and normal pupillary response. References: Diplopia and ptosis. Diagnosis: diabetic third nerve palsy. (http://www.ncbi.nlm.nih.gov/pubmed/20642274)

A 64-Year-Old Woman Is Brought to the Emergency Department Due