A 32-year-old woman comes to the office due to left eye pain that is accentuated by ocular movements. She also has periodic dimming of vision in the same eye. The patient has had several such episodes over the last month, most often after a hot shower or intense workout. A year ago, she had an episode of numbness and tingling in her left arm that resolved spontaneously. The patient has no other medical issues and takes no medication. She smokes half a pack of cigarettes a day and does not use alcohol or illicit drugs. Vital signs are normal. BMI is 26 kg/m². Ophthalmologic examination shows swelling of the optic disc on the left. Neurologic examination shows a mild intention tremor and broad-based gait. Which of the following is the most likely cause of the patient's current condition?

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11ec160b_39d0_0d2f_9249_a17cdd4136b8_MD0001_00 This patient has eye pain worsened with movement, intermittently decreased vision, and swelling of the optic disc, consistent with optic neuritis. In a young female patient, optic neuritis should raise concern for multiple sclerosis (MS), a chronic immune-mediated disease that affects the central nervous system (CNS) and leads to oligodendrocyte destruction. Demyelinating plaques are commonly seen as hyperintense lesions on T2- weighted MRI of the brain and spinal cord. MS is characterized by episodic, progressive neurologic deficits that may involve multiple anatomic regions within the CNS (ie, separated in space and time). In addition to optic neuritis, other manifestations of MS include sensory/motor symptoms (eg, arm numbness and tingling), internuclear ophthalmoplegia, cerebellar dysfunction (eg, intention tremor, broad-based gait), fatigue, and Lhermitte sign (electrical sensations down the back/limbs with neck flexion). Symptom worsening can occur with increased body temperature (eg, exercise, bathing) due to slowing of neuronal conduction in unmyelinated nerves (Uhthoff phenomenon). (Choice A) Atherosclerosis of the carotid arteries can cause transient ischemia leading to episodic vision loss (amaurosis fugax). However, it would not typically cause eye pain or worsening symptoms with body heat, and would be rare in a young patient without other signs of atherosclerosis. (Choice B) Brain metastases can cause a variety of neurologic symptoms (eg, cerebellar signs, vision changes) but would be expected to worsen with time, not relapse and remit. (Choice D) Polycythemia vera can cause transient visual disturbances and other neurologic manifestations due to increased blood viscosity. Although patients may have pruritus or erythema following heat exposure, heat does not worsen neurologic symptoms. Also, this patient does not have other polycythemic manifestations (eg, hypertension, facial plethora). (Choice E) Neurosyphilis can cause a wide-based gait and pupillary irregularities (Argyll Robertson pupil; ie, accommodates but does not react to light), but there is no pain with eye movement or vision loss. In addition, heat sensitivity and upper extremity weakness would be unexpected. (Choice F) Vitamin B₁₂ deficiency causes subacute combined degeneration, and patients can develop a broad-based gait. However, in most cases this is slowly progressive and often accompanied by paresthesias in the distal lower extremities. Intention tremor and optic neuritis are not associated with vitamin B₁₂ deficiency. Educational objective: Multiple sclerosis is characterized by episodic, progressive neurologic deficits involving multiple anatomic regions within the central nervous system. Demyelinating plaques are commonly seen as hyperintense lesions on T2-weighted MRI of the brain and spinal cord. Common manifestations include optic neuritis, internuclear ophthalmoplegia, sensory deficits, and fatigue, which may worsen with heat exposure. __________ References: Advances in the immunopathogenesis of multiple sclerosis. (http://www.ncbi.nlm.nih.gov/pubmed/25887768)

A 32-Year-Old Woman Comes to the Office Due to Left