A 25-year-old woman comes to the office due to intermittent double vision, dizziness, and unsteady gait for the last several days. During the past year, she has had several episodes of numbness and dizziness, and her symptoms were attributed to anxiety. She does not use tobacco or alcohol. Her brother died of subarachnoid hemorrhage. Blood pressure is 130/70 mm Hg and pulse is 76/min. On attempted left gaze, her left eye abducts and exhibits horizontal nystagmus, but her right eye remains stationary. When she attempts to look to the right, her right eye abducts and exhibits horizontal nystagmus, but her left eye remains stationary. The patient is able to converge both eyes without any associated nystagmus. Which of the following is the most likely site of the lesion in this patient?

Question

A 25-year-old woman comes to the office due to intermittent double vision, dizziness, and unsteady gait for the last several days.  During the past year, she has had several episodes of numbness and dizziness, and her symptoms were attributed to anxiety.  She does not use tobacco or alcohol.  Her brother died of subarachnoid hemorrhage.  Blood pressure is 130/70 mm Hg and pulse is 76/min.  On attempted left gaze, her left eye abducts and exhibits horizontal nystagmus, but her right eye remains stationary.  When she attempts to look to the right, her right eye abducts and exhibits horizontal nystagmus, but her left eye remains stationary.  The patient is able to converge both eyes without any associated nystagmus.  Which of the following is the most likely site of the lesion in this patient?

Quizplus · Accepted Answer

11ec25c8_d14a_0a20_bc81_5bc6588901e8_MD0003_00 This young woman with neurologic deficits disseminated in space and time (eg, diplopia, ataxia, vertigo, numbness) most likely has multiple sclerosis, an inflammatory demyelinating disorder characterized by white matter lesions in the central nervous system. Her pattern of eye movement dysfunction is consistent with internuclear ophthalmoplegia, a disorder of conjugate horizontal gaze in which the affected eye (ipsilateral to the lesion) is unable to adduct and the contralateral eye abducts with nystagmus. Convergence and the pupillary light reflex are preserved. conjugate horizontal gaze Internuclear ophthalmoplegia results from damage to the heavily myelinated fibers of the medial longitudinal fasciculus (MLF). The MLF is a paired neural tract that mediates communication between CN III (oculomotor) and CN VI (abducens) nuclei, allowing for coordinated horizontal eye movements. Unilateral MLF lesions can occur with lacunar stroke in the pontine artery distribution; however, bilateral lesions are classically seen in multiple sclerosis. (Choice A) A lesion of the abducens nerve would result in a lateral rectus palsy with inability to abduct the eye. (Choice B) The Edinger-Westphal nucleus provides preganglionic parasympathetic outflow to the eye. Damage to this structure would result in an ipsilateral fixed and dilated pupil that is nonreactive to light or accommodation. Edinger-Westphal nucleus (Choice C) Myasthenia gravis is characterized by antibody-mediated destruction of acetylcholine receptors at the motor end plate. Patients typically present with fluctuating and fatigable ocular (eg, diplopia, ptosis) and bulbar weakness (eg, dysphagia). Internuclear ophthalmoplegia is not characteristic. (Choice D) The lateral geniculate nucleus is located in the thalamus and relays visual information to the ipsilateral primary visual cortex. Damage to this structure would result in a contralateral homonymous hemianopsia. (Choice E) A lesion of the medial lemniscus would result in contralateral loss of vibration, proprioception, and light touch. (Choice G) Oculomotor nerve palsy is characterized by mydriasis, ptosis, and "down and out" deviation of the ipsilateral eye. This may occur with nerve compression (eg, posterior communicating artery aneurysm) or microvascular nerve ischemia (eg, diabetes mellitus). Nerve compression is more likely to cause mydriasis as parasympathetic fibers are situated on the periphery of the oculomotor nerve. (Choice H) A lesion of the optic chiasm would result in bitemporal hemianopsia. This may occur with anterior communicating artery aneurysms or tumors within the sella turcica (eg, craniopharyngioma, pituitary adenoma). (Choice I) A lesion of the optic nerve (eg, optic neuritis) would result in monocular vision loss. (Choice J) Trochlear nerve palsy is typically traumatic or idiopathic and presents with vertical diplopia that worsens when the affected eye looks down and toward the nose (eg, walking downstairs, reading). Patients may compensate by tucking the chin and tilting the head away from the affected eye. Educational objective: Internuclear ophthalmoplegia is a disorder of conjugate horizontal gaze that results from damage to the medial longitudinal fasciculus (MLF). The affected eye (ipsilateral to the lesion) is unable to adduct and the contralateral eye abducts with nystagmus. Unilateral MLF lesions can occur with lacunar stroke in the pontine artery distribution; however, bilateral lesions are classically seen in multiple sclerosis. References: Images in clinical medicine. Bilateral internuclear ophthalmoplegia in multiple sclerosis. (http://www.ncbi.nlm.nih.gov/pubmed/23323922) Internuclear ophthalmoplegia: MR-anatomic correlation. (http://www.ncbi.nlm.nih.gov/pubmed/3105283)

A 25-Year-Old Woman Comes to the Office Due to Intermittent