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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{YD}} (Reviewed by  {{YD}} and  {{AJL}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
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|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Hematology
|SubCategory=Hematology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
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|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Hematology
|SubCategory=Hematology
|Prompt=A 25 year old male patient, previously healthy, presents to the physician's office complaining of blistering vesicles over different parts of his body. He reports that he has had previous episodes in the past, all of which occur following exposure to sunlight. The patient then adds that he also notices that his urine has a reddish brown discoloration under natural light. Based on the simplified diagram of heme synthesis shown 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 face and 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 is presenting with porphyria cutanea tarda (PCT). Porphyria cutanea tarda is characterized by the deficiency of the enzyme uroporphyrinogen decarboxylase. In PCT, patients typically have acute skin eruptions of blistering vesicles that occupy different parts of the patient's body. These vesicles appear in sun-exposed areas and are exacerbated by sunlight and typically arise a few days after exposure to sun. Due to increased levels of uroporphyrinogen in the urine, the color of the urine becomes reddish brown under natural light and pinkish under Wood's lamp. PCT may be familial or sporadic. Sun avoidance, and reduction of iron stores (phlebotomy and chelation) are important in the management of the patient.
|Explanation=[[Porphyria cutanea tarda]] (PCT) is caused by the deficiency of the enzyme uroporphyrinogen decarboxylase. Patients with PCT typically present with acute skin eruptions of blistering vesicles that are usually located on the face and upper extremities (sun-exposed body areas) but may also be present different parts of the body a few days following sun exposure. Due to increased concentration of uroporphyrinogen in the urine, the urine appears reddish brown under natural light and pinkish under Wood's lamp. Sun avoidance and reduction of iron stores (phlebotomy and chelation) are important measures in the management of patients with PCT.
 
(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.
 
Reference:
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, deficient in B6 deficiency.
|AnswerAExp="A" corresponds to ALA synthase. ALA synthase activity is deficient in [[B6 deficiency]].
|AnswerB=B
|AnswerB=B
|AnswerBExp="B" corresponds to ALA dehydratase, deficient in lead toxicity.
|AnswerBExp="B" corresponds to ALA dehydratase. ALA dehydratase activity is deficient in [[lead toxicity]].
|AnswerC=C
|AnswerC=C
|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, which is not clinically relevant.
|AnswerDExp="D" corresponds to uroporphyrinogen III synthase. Uroporphyrinogen III synthase deficiency is associated with [[Gunther disease]] (congenital erythropoietic porphyria).
|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]] (PCT) is caused 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.<br>
First Aid 2014 page 388
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=porphyria, cutanea, tarda, PCT, photosensitivity, urine, pink, pinkish, red, reddish, brown, brownish, color, discoloration, uroporphyrinogen, decarboxylase, blister, vesicle, blisters, vesicles, heme, pathway, Wood, Wood's, lamp, ultraviolet
|WBRKeyword=Porphyria cutanea tarda, PCT, Photosensitivity, Uroporphyrinogen decarboxylase, Urine discoloration, Uroporphyrinogen, Decarboxylase, Blisters, Vesicles, Heme synthesis pathway, Wood's lamp
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 00:15, 28 October 2020
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 face and 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 deficient in B6 deficiency.]]
Answer B AnswerB::B
Answer B Explanation [[AnswerBExp::"B" corresponds to ALA dehydratase. ALA dehydratase activity is deficient 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 disease (congenital erythropoietic porphyria).]]
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 caused by the deficiency of the enzyme uroporphyrinogen decarboxylase. Patients with PCT typically present with acute skin eruptions of blistering vesicles that are usually located on the face and upper extremities (sun-exposed body areas) but may also be present different parts of the body a few days following sun exposure. Due to increased concentration of uroporphyrinogen in the urine, the urine appears reddish brown under natural light and pinkish under Wood's lamp. Sun avoidance and reduction of iron stores (phlebotomy and chelation) are important measures in the management of patients with PCT.

Educational Objective: Porphyria cutanea tarda (PCT) is caused 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.
First Aid 2014 page 388]]

Approved Approved::Yes
Keyword WBRKeyword::Porphyria cutanea tarda, WBRKeyword::PCT, WBRKeyword::Photosensitivity, WBRKeyword::Uroporphyrinogen decarboxylase, WBRKeyword::Urine discoloration, WBRKeyword::Uroporphyrinogen, WBRKeyword::Decarboxylase, WBRKeyword::Blisters, WBRKeyword::Vesicles, WBRKeyword::Heme synthesis pathway, WBRKeyword::Wood's lamp
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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