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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor=Vendhan Ramanujam
|QuestionAuthor= {{Rim}} (Reviewed by  {{AJL}} and  {{YD}})
|ExamType=USMLE Step 2 CK
|ExamType=USMLE Step 1
|MainCategory=Internal medicine
|MainCategory=Pathology
|SubCategory=Endocrine
|SubCategory=Gastrointestinal
|MainCategory=Internal medicine
|MainCategory=Pathology
|SubCategory=Endocrine
|SubCategory=Gastrointestinal
|MainCategory=Internal medicine
|MainCategory=Pathology
|SubCategory=Endocrine
|SubCategory=Gastrointestinal
|MainCategory=Internal medicine
|MainCategory=Pathology
|MainCategory=Internal medicine
|MainCategory=Pathology
|SubCategory=Endocrine
|MainCategory=Pathology
|MainCategory=Internal medicine
|SubCategory=Gastrointestinal
|SubCategory=Endocrine
|MainCategory=Pathology
|MainCategory=Internal medicine
|SubCategory=Gastrointestinal
|SubCategory=Endocrine
|MainCategory=Pathology
|MainCategory=Internal medicine
|SubCategory=Gastrointestinal
|SubCategory=Endocrine
|MainCategory=Pathology
|MainCategory=Internal medicine
|SubCategory=Gastrointestinal
|MainCategory=Internal medicine
|MainCategory=Pathology
|SubCategory=Endocrine
|MainCategory=Pathology
|Prompt=A 30 year old male presents with fatigue, decreased appetite, weight gain, constipation and cold intolerance.  He recalls no event of stress. He does not take any medications. He is a non-smoker and a non alcoholic. His pulse is 48/min and blood pressure is 146/90 mmHg. Physical examination reveals cold extremities, pale skin, coarse hair and brittle nails. There is delayed relaxation of deep tendon reflexes.  The thyroid gland is normal on palpitation.  Laboratory studies reveal increased serum free T3 and T4 but normal serum TSH level.  Which is the most likely diagnosis?
|SubCategory=Gastrointestinal
|Explanation=Besides primary, secondary and tertiary [[hypothyroidism]], rarely [[Thyroid hormone resistance|generalized resistance to thyroid hormones]] may cause hypothyroidism. Generalized resistance to thyroid hormones results from a receptor defect in the peripheral tissues. They usually present at an early age with growth and mental retardation, however patients with milder defects can present later in life.  Elevated circulating [[thyroid hormone]] levels with normal or elevated [[TSH]] levels are characteristic. They present with hypothyroidism despite having elevated thyroid hormone levels.
|Prompt=A 62-year-old man presents to the physician's office with complaints of worsening abdominal pain over the past four months. The pain is described as dull and localized in the mid-epigastric region. The patient denies any association between his pain and food intake or posture. Upon further questioning, he describes symptoms of increasing fatigue and recent unintentional weight loss. An abdominal CT scan shows a gastric mass, and an endoscopy-guided biopsy of the mass reveals clusters of thin, elongated, spindle cells. Immunohistochemistry of this patient's tumor is most likely to reveal expression of which protein?
 
|Explanation=Gastrointestinal stromal tumor (GIST) is a rare non-epithelial neoplasm of the GI tract, the mesentary, or the omentum. The majority of GIST tumors are spindle cell tumors that may be either malignant or benign. Most stromal tumors stain positively for C-Kit/CD117 (>90%), CD34, muscle-specific actin, smooth muscle actin, S-100, and desmin. Patients with GIST may be asymptomatic or have non-specific GI symptoms. This patient's symptoms of dull epigastric pain, fatigue, and weight loss, in conjunction with the CT finding of a mass in the stomach, are suggestive of malignancy. Characteristically, the pathogenesis of GIST tumors involves a gain-of-function mutation in the ''KIT'' proto-oncogene, which encodes a transmembrane receptor for stem cell factor that includes a tyrosine kinase component in its intracytoplasmic region.
'''Educational Objective:'''
|AnswerA=C-kit
Elevated circulating thyroid hormone levels with normal or elevated TSH levels with features of hypothyroidism can happen in generalized resistance to thyroid hormones.  
|AnswerAExp=Expression of [[C-kit]] is associated with [[GIST]].
|AnswerA=Subclinical hypothyroidism
|AnswerB=Ret
|AnswerBExp=Expression of Ret protein is associated with multiple endocrine neoplasia (MEN) 2A and 2B syndromes.
|AnswerAExp='''Incorrect'''-Mildly elevated serum TSH levels and normal circulating thyroid hormone levels characterize subclinical hypothyroidism.  Patients do not have clinical features of hypothyroidism.  
|AnswerC=Braf
|AnswerB=Primary hypothyroidism
|AnswerCExp=Expression of Braf is associated with melanoma
|AnswerBExp='''Incorrect'''-Low circulating levels of thyroid hormones with TSH levels more than 10 IU/L characterizes primary hypothyroidism.  
|AnswerD=Ras
|AnswerC=Central hypothyroidism
|AnswerDExp=Expression of Ras is associated with colon adenocarcinoma.
|AnswerCExp='''Incorrect'''-Secondary and tertiary are central hypothyroidism.  Low circulating thyroid hormone levels with low or inappropriate normal TSH levels characterize them.
|AnswerE=C-myc
|AnswerD=Sick euthyroid syndrome
|AnswerEExp=Expression of [[C-myc]] is associated with [[Burkitt's lymphoma]].
|AnswerDExp='''Incorrect'''-In [[Euthyroid sick syndrome|sick euthyroid syndrome]], the abnormality pattern is usually a low total or free T3 level with normal T4 and TSH levels, due to decrease in the peripheral conversion of T4 to T3 following a severe illness.  
|EducationalObjectives=Gastrointestinal stromal tumor (GIST) is a rare non-epithelial neoplasm of the GI tract, the mesentary, or the omentum. The majority of GIST tumors are spindle cell tumors that may be either malignant or benign. Most stromal tumors stain positively for C-Kit/CD117
|AnswerE=Generalized resistance to thyroid hormones
|References=Din OS, Woll PJ. Treatment of gastrointestinal stromal tumor: focus on imatinib mesylate. Ther Clin Risk Manag. 2008;4(1):149-62.<br>
 
First Aid 2014 page 232
|AnswerEExp='''Correct'''-Besides primary, secondary and tertiary hypothyroidism, rarely generalized resistance to thyroid hormones may cause hypothyroidism. Generalized resistance to thyroid hormones results from a receptor defect in the peripheral tissues. They usually present at an early age with growth and mental retardation, however patients with milder defects can present later in life. Elevated circulating thyroid hormone levels with normal or elevated TSH levels are characteristic. They present with hypothyroidism despite having elevated thyroid hormone levels.
|RightAnswer=A
|RightAnswer=E
|WBRKeyword=Cancer, GIST, Gastrointestinal stromal tumor, Marker, Mutation, KIT, C-kit, Proto-oncogene, Immunohistochemistry
|Approved=Yes
|Approved=Yes
}}
}}

Latest revision as of 23:54, 27 October 2020
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz [2] and Yazan Daaboul, M.D.)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pathology
Sub Category SubCategory::Gastrointestinal
Prompt [[Prompt::A 62-year-old man presents to the physician's office with complaints of worsening abdominal pain over the past four months. The pain is described as dull and localized in the mid-epigastric region. The patient denies any association between his pain and food intake or posture. Upon further questioning, he describes symptoms of increasing fatigue and recent unintentional weight loss. An abdominal CT scan shows a gastric mass, and an endoscopy-guided biopsy of the mass reveals clusters of thin, elongated, spindle cells. Immunohistochemistry of this patient's tumor is most likely to reveal expression of which protein?]]
Answer A AnswerA::C-kit
Answer A Explanation [[AnswerAExp::Expression of C-kit is associated with GIST.]]
Answer B AnswerB::Ret
Answer B Explanation AnswerBExp::Expression of Ret protein is associated with multiple endocrine neoplasia (MEN) 2A and 2B syndromes.
Answer C AnswerC::Braf
Answer C Explanation AnswerCExp::Expression of Braf is associated with melanoma
Answer D AnswerD::Ras
Answer D Explanation AnswerDExp::Expression of Ras is associated with colon adenocarcinoma.
Answer E AnswerE::C-myc
Answer E Explanation [[AnswerEExp::Expression of C-myc is associated with Burkitt's lymphoma.]]
Right Answer RightAnswer::A
Explanation [[Explanation::Gastrointestinal stromal tumor (GIST) is a rare non-epithelial neoplasm of the GI tract, the mesentary, or the omentum. The majority of GIST tumors are spindle cell tumors that may be either malignant or benign. Most stromal tumors stain positively for C-Kit/CD117 (>90%), CD34, muscle-specific actin, smooth muscle actin, S-100, and desmin. Patients with GIST may be asymptomatic or have non-specific GI symptoms. This patient's symptoms of dull epigastric pain, fatigue, and weight loss, in conjunction with the CT finding of a mass in the stomach, are suggestive of malignancy. Characteristically, the pathogenesis of GIST tumors involves a gain-of-function mutation in the KIT proto-oncogene, which encodes a transmembrane receptor for stem cell factor that includes a tyrosine kinase component in its intracytoplasmic region.

Educational Objective: Gastrointestinal stromal tumor (GIST) is a rare non-epithelial neoplasm of the GI tract, the mesentary, or the omentum. The majority of GIST tumors are spindle cell tumors that may be either malignant or benign. Most stromal tumors stain positively for C-Kit/CD117
References: Din OS, Woll PJ. Treatment of gastrointestinal stromal tumor: focus on imatinib mesylate. Ther Clin Risk Manag. 2008;4(1):149-62.
First Aid 2014 page 232]]

Approved Approved::Yes
Keyword WBRKeyword::Cancer, WBRKeyword::GIST, WBRKeyword::Gastrointestinal stromal tumor, WBRKeyword::Marker, WBRKeyword::Mutation, WBRKeyword::KIT, WBRKeyword::C-kit, WBRKeyword::Proto-oncogene, WBRKeyword::Immunohistochemistry
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