WBR0149

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A 35-year-old woman presents to her ophthalmologist for impaired dark adaptation. Over the past month she has experienced increasing difficulty distinguishing objects, especially when driving home from work at night. Her past medical history is significant for severe Crohn's disease. She denies any family history of ocular disease. She reports her family history is only significant for essential hypertension in her father and dyslipidemia in her mother. On physical examination, the physician notes white patches on the oral mucosa. What is the most likely diagnosis?]]
Answer A	AnswerA::Diabetic retinopathy
Answer A Explanation	[[AnswerAExp::Diabetic retinopathy is the most severe retinal complication of diabetes mellitus. It is the leading cause of non-traumatic blindness in adults. People with untreated diabetes are 25 times more likely to develop blindness than the general population. However, this patient is young and neither her medical history nor her symptoms suggest the presence of diabetes. Screening for diabetic retinopathy is regularly performed for patients with type 1 and type 2 diabetes mellitus.]]
Answer B	AnswerB::Glaucoma
Answer B Explanation	[[AnswerBExp::Glaucoma is a group of diseases of the optic nerve involving loss of retinal ganglion cells in a characteristic pattern. Although raised intraocular pressure is a significant risk factor for developing glaucoma, there is no established threshold intraocular pressure that causes glaucoma. Untreated glaucoma leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness. This patient has no history of conditions, such as ocular trauma or uveitis, that would increase clinical suspicion for glaucoma.]]
Answer C	AnswerC::Cataract
Answer C Explanation	[[AnswerCExp::Cataract is an opacity that develops in the crystalline lens of the eye or in its envelope. Cataract can be caused by several causes, including advanced age and diabetes mellitus. However, this patient is young and her clinical history does not suggest the presence of cataract.]]
Answer D	AnswerD::Vitamin deficiency
Answer D Explanation	AnswerDExp::Night blindness is one of the first signs of vitamin A deficiency. Vitamin A deficiency is common among patients with malabsorptive conditions, such as Crohn's disease.
Answer E	AnswerE::Genetic disease
Answer E Explanation	[[AnswerEExp::Genetic causes of blindness include: Leber's congenital amaurosis, Leber's hereditary optic neuropathy, and retinoblastoma and albinism. This patient has no family history of blindness or albinism. Furthermore, she is older than the typical age of onset of all of the above conditions.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::Vitamin A deficiency is common among children, women of reproductive age, and patients with malabsorptive diseases such as Crohn's disease. Bilateral night blindness (nyctalopia) is one of the first signs of vitamin A deficiency. Vitamin A is a critical precursor involved in the synthesis of rhodopsin, the eye pigment responsible for sensing light. Rhodopsin is composed of retinal (an activated form of vitamin A) and opsin (a protein). When vitamin A is not present in sufficient quantities, deficiency of retinal leads to deficiency of fully assembled rhodopsin. The eye becomes more poorly suited to adapt to low-illumination scenarios, resulting in night blindness. In addition to its essential structural role in rhodopsin, vitamin A is necessary for cellular differentiation in the immune system and maintenance of the skin epithelium. As a result, vitamin A deficiency is associated with dry, thickened skin, white patches on oral mucosa due to keratinization of mucous membranes, and increased risk of infection, particularly with measles. Additionally, vitamin A has a role in the treatment of acute promyelocytic leukemia, which is caused by a translocation of the retinoic acid (a metabolite of vitamin A) receptor that induces a differentiation block in myeloid progenitors. Acute promyelocytic leukemia can be treated with a combination of all-trans-retinoic acid and arsenic. Educational Objective: Bilateral night blindness (nyctalopia) is usually the first symptom of vitamin A deficiency. Children, women of reproductive age, and individuals with malabsorptive conditions such as Crohn's disease are highest risk of developing vitamin A deficiency. References: Main AN, Mills PR, Russell RI, et al. Vitamin A deficiency in Crohn's disease. Gut. 1983;24(12):1169-75. da Rocha Lima B, Pichi F, Lowder CY. Night blindness and Crohn's disease. Int Ophthalmol. 2014;34(5):1141-4. First Aid 2014 page 92]]
Approved	Approved::Yes
Keyword	WBRKeyword::Eye, WBRKeyword::Opthalmology, WBRKeyword::Blindness, WBRKeyword::Vitamin, WBRKeyword::Nutrition, WBRKeyword::Vision loss, WBRKeyword::Vitamin A deficiency, WBRKeyword::Crohn's disease, WBRKeyword::Crohn, WBRKeyword::Malabsorption, WBRKeyword::Malabsorptive disease
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