WBR0597

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry, MainCategory::Pathophysiology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 74 year old male patient presents to the physician's office with a clouded dim vision. The patient further explains that he has difficulty seeing objects at night and sees normal lights too bright. His symptoms have been gradually worsening. His past medical history is significant for coronary artery disease (CAD), uncontrolled type 2 diabetes mellitus on daily insulin injections, hypertension on metoprolol and lisinopril, and dyslipidemia on atorvastatin. When asked, the physician explains to the patient the etiology of the patient's symptoms. Which of the following is true regarding the pathophysiology of the patient's condition?]]
Answer A	AnswerA::Optic disc swelling that causes an elevation in intracranial pressure
Answer A Explanation	[[AnswerAExp::Papilledema is characterized by optic disc swelling that causes an elevation in intracranial pressure. It may be asymptomatic or may present with visual and extravisual symptoms. Visual symptoms include transient visual flickering, blurring of vision and constricted visual field, diplopia, decreased perception of color. Extravisual symptoms include headache, pulsatile tinnitus, nausea, and vomiting that often occur secondary to increased intracranial pressure.]]
Answer B	AnswerB::Absence of a key transfer enzyme and subsequent shunting of the pathway towards the formation of galactitol
Answer B Explanation	[[AnswerBExp::Classic galactosemia is an autosomal recessive disorder characterized by the absence of galactose-1-phosphate uridyltransferase enzyme and and subsequent shunting of the galactose metabolism pathway towards the formation of galactitol. It usually causes infantile cataracts; it is unusual to present in this elderly patient.]]
Answer C	AnswerC::Accumulation of glucose by-products in organs that lack enzymes that normally allow oxidation to fructose
Answer C Explanation	AnswerCExp::Cataract is caused by sorbitol accumulation in diabetic patients.
Answer D	AnswerD::A bilateral lesion at the level of the Meyer's loop in the cerebral cortex
Answer D Explanation	[[AnswerDExp::Meyer's loop, located in the temporal lobe, is a special region of the visual pathway. If lesioned, the patient will complain of superior homonymous quadrantanopia. In the unlikely event of bilateral lesions, the expected visual loss would be vision loss of the superior half of the visual field.]]
Answer E	AnswerE::Degeneration of the central region of the retina due to accumulation of deposited material in the extracellular region beneath the retinal pigmented epithelium
Answer E Explanation	[[AnswerEExp::Macular degeneration is the degeneration of the central region within the retina due to extracellular deposition of material beneath the retinal pigmented epithelium. Age-related macular denegeration (ARMD) is the leading cause of blindness in America in patients above 60 years of age. Patients usually present with an increase in the number of floaters, flashes of light on peripheral vision with a positive Amsler grid test. The latter is a grid that uses horizontal and vertical lines and a small dot in the center. The patient looks at with each eye separately. A positive (abnormal) test is when the patient sees the straight lines as curved. Positive Amsler test usually signifies the presence of a retinal disease, such as ARMD.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Cataracts is a common pathology in diabetic patients. It is a result of accumulation of sorbitol, that is produced from glucose by the action of aldose reductase. Some organs, like the eye retina, the kidney, and schwann cells of the nervous system are especially susceptible to sorbitol accumulation because they normally lack the enzyme that may deplete sorbitol by an oxidation process using sorbitol dehydrogenase to form fructose. Cataract is caused by the opacification of the lens. It is usually painless and occurs bilaterally. Classical symptoms are progressive visual loss, clouding of vision, and glare when looking at lights that appear abnormally bright. Educational Objective: Sorbitol accumulation in organs that lack sorbitol dehydrogenase to form fructose from glucose is often found in patients with diabetes mellitus and causes cataract. References: First Aid 2014 page 107]]
Approved	Approved::No
Keyword	WBRKeyword::cataract, WBRKeyword::sorbitol, WBRKeyword::galactitol, WBRKeyword::opacification, WBRKeyword::lens, WBRKeyword::visual, WBRKeyword::field, WBRKeyword::visual disturbance, WBRKeyword::disturbance, WBRKeyword::painless, WBRKeyword::diabetes mellitus, WBRKeyword::diabetes, WBRKeyword::mellitus, WBRKeyword::accumulation, WBRKeyword::glucose, WBRKeyword::fructose, WBRKeyword::Amsler, WBRKeyword::test, WBRKeyword::Amsler test
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