WBR0347: Difference between revisions

Jump to navigation Jump to search
VisualWikitext
No edit summary
No edit summary
Line 1: Line 1:
{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}} {{Alison}}
|QuestionAuthor={{YD}} (Reviewed by {{YD}} and {{AJL}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
Line 8: Line 8:
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Hematology
|SubCategory=Hematology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
Line 20: Line 21:
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Hematology
|SubCategory=Hematology
|Prompt=A 25-year-old male presents to the physician's office with complaints of blistering vesicles on various parts of his body. He reports that he had previous episodes, all of which occured following exposure to sunlight, and that his urine has a reddish brown discoloration under natural light. Based on the simplified diagram of heme synthesis illustrated below, which of the following steps is most likely inhibited in this patient?
|Prompt=A 25-year-old man presents to the physician's office with complaints of blistering vesicles on his upper extremities. He reports that he previously had similar episodes in the pasts, all of which occurred following exposure to sunlight. The patient also states that his urine has a reddish brown discoloration under natural light. Based on the simplified diagram of heme synthesis illustrated below, which of the following steps is most likely inhibited in this patient?


[[Image:WBR0344.png|500px]]
[[Image:WBR0344.png|500px]]
|Explanation=The patient in this scenario most likely has [[porphyria cutanea tarda]] (PCT). [[Porphyria cutanea tarda]], which may be familial or sporadic, is characterized by the deficiency of the enzyme uroporphyrinogen decarboxylase. In PCT, patients typically present with acute skin eruptions of blistering vesicles, which occupy different parts of the body. Typically appearing a few days following sun exposure, these vesicles are exacerbated by sunlight. Due to increased levels of uroporphyrinogen in the urine, the urine becomes reddish brown under natural light and pinkish under Wood's lamp. Sun avoidance, and reduction of iron stores (phlebotomy and chelation) are important in the management of the patient.
|Explanation=[[Porphyria cutanea tarda]] (PCT) is characterized by the deficiency of the enzyme uroporphyrinogen decarboxylase. Patients with PCT typically present with acute skin eruptions of blistering vesicles, which typically occupy the distal upper extremities but may also include different parts of the body that are exposed to sun. Typically appearing a few days following sun exposure, these vesicles are exacerbated by sunlight. Due to increased levels of uroporphyrinogen in the urine, the urine becomes reddish brown under natural light and pinkish under Wood's lamp. Sun avoidance, and reduction of iron stores (phlebotomy and chelation) are important in the management of the patient.


(To note, the image above is simplified. Some intermediate products and enzymes are not listed in this illustration of heme synthesis).
(To note, the image above is simplified. Some intermediate products and enzymes are not listed in this illustration of heme synthesis).
|EducationalObjectives= [[Porphyria cutanea tarda]] is characterized by a deficiency of uroporphyrinogen decarboxylase.
|References= Munoz-Santos C, Guilabert A, Monero N, et al. Familial and sporadic porphyria cutanea tarda: clinical and biochemical features and risk factors in 152 patients. Medicine (Baltimore). 2010;89(2):69-74.
|AnswerA=A
|AnswerA=A
|AnswerAExp="A" corresponds to ALA synthase. ALA synthase activity is decreased in [[B6 deficiency]].
|AnswerAExp="A" corresponds to ALA synthase. ALA synthase activity is decreased in [[B6 deficiency]].
Line 38: Line 34:
|AnswerCExp="C" corresponds to porphobilinogen deaminase, deficient in acute intermittent [[porphyria]].
|AnswerCExp="C" corresponds to porphobilinogen deaminase, deficient in acute intermittent [[porphyria]].
|AnswerD=D
|AnswerD=D
|AnswerDExp="D" corresponds to uroporphyrinogen III synthase. Uroporphyrinogen III synthase deficiency is associated with [[Gunther's disease]].  
|AnswerDExp="D" corresponds to uroporphyrinogen III synthase. Uroporphyrinogen III synthase deficiency is associated with [[Gunther's disease]].
|AnswerE=E
|AnswerE=E
|AnswerEExp="E" corresponds to uroporphyrinogen decarboxylase, deficient in [[Porphyria cutanea tarda]] (PCT).
|AnswerEExp="E" corresponds to uroporphyrinogen decarboxylase, deficient in [[Porphyria cutanea tarda]] (PCT).
|EducationalObjectives=[[Porphyria cutanea tarda]] is characterized by a deficiency of uroporphyrinogen decarboxylase.
|References=Munoz-Santos C, Guilabert A, Monero N, et al. Familial and sporadic porphyria cutanea tarda: clinical and biochemical features and risk factors in 152 patients. Medicine (Baltimore). 2010;89(2):69-74.
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=porphyria, cutanea, tarda, PCT, photosensitivity, urine discoloration, uroporphyrinogen, decarboxylase, blisters, vesicles, heme pathway, Wood's lamp, ultraviolet
|WBRKeyword=porphyria, cutanea, tarda, PCT, photosensitivity, urine discoloration, uroporphyrinogen, decarboxylase, blisters, vesicles, heme pathway, Wood's lamp, ultraviolet
|Approved=Yes
|Approved=Yes
}}
}}

Revision as of 17:10, 2 February 2015
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pathophysiology
Sub Category SubCategory::Hematology
Prompt [[Prompt::A 25-year-old man presents to the physician's office with complaints of blistering vesicles on his upper extremities. He reports that he previously had similar episodes in the pasts, all of which occurred following exposure to sunlight. The patient also states that his urine has a reddish brown discoloration under natural light. Based on the simplified diagram of heme synthesis illustrated below, which of the following steps is most likely inhibited in this patient?

]]

Answer A AnswerA::A
Answer A Explanation [[AnswerAExp::"A" corresponds to ALA synthase. ALA synthase activity is decreased in B6 deficiency.]]
Answer B AnswerB::B
Answer B Explanation [[AnswerBExp::"B" corresponds to ALA dehydratase. ALA dehydratase activity is decreased in lead toxicity.]]
Answer C AnswerC::C
Answer C Explanation [[AnswerCExp::"C" corresponds to porphobilinogen deaminase, deficient in acute intermittent porphyria.]]
Answer D AnswerD::D
Answer D Explanation [[AnswerDExp::"D" corresponds to uroporphyrinogen III synthase. Uroporphyrinogen III synthase deficiency is associated with Gunther's disease.]]
Answer E AnswerE::E
Answer E Explanation [[AnswerEExp::"E" corresponds to uroporphyrinogen decarboxylase, deficient in Porphyria cutanea tarda (PCT).]]
Right Answer RightAnswer::E
Explanation [[Explanation::Porphyria cutanea tarda (PCT) is characterized by the deficiency of the enzyme uroporphyrinogen decarboxylase. Patients with PCT typically present with acute skin eruptions of blistering vesicles, which typically occupy the distal upper extremities but may also include different parts of the body that are exposed to sun. Typically appearing a few days following sun exposure, these vesicles are exacerbated by sunlight. Due to increased levels of uroporphyrinogen in the urine, the urine becomes reddish brown under natural light and pinkish under Wood's lamp. Sun avoidance, and reduction of iron stores (phlebotomy and chelation) are important in the management of the patient.

(To note, the image above is simplified. Some intermediate products and enzymes are not listed in this illustration of heme synthesis).
Educational Objective: Porphyria cutanea tarda is characterized by a deficiency of uroporphyrinogen decarboxylase.
References: Munoz-Santos C, Guilabert A, Monero N, et al. Familial and sporadic porphyria cutanea tarda: clinical and biochemical features and risk factors in 152 patients. Medicine (Baltimore). 2010;89(2):69-74.]]

Approved Approved::Yes
Keyword WBRKeyword::porphyria, WBRKeyword::cutanea, WBRKeyword::tarda, WBRKeyword::PCT, WBRKeyword::photosensitivity, WBRKeyword::urine discoloration, WBRKeyword::uroporphyrinogen, WBRKeyword::decarboxylase, WBRKeyword::blisters, WBRKeyword::vesicles, WBRKeyword::heme pathway, WBRKeyword::Wood's lamp, WBRKeyword::ultraviolet
Linked Question Linked::
Order in Linked Questions LinkedOrder::
Retrieved from "https://www.wikidoc.org/index.php?title=WBR0347&oldid=1061845"