WBR0079

Author	[[PageAuthor::Mohamed Moubarak, M.D. [1]]]
Exam Type	ExamType::USMLE Step 3
Main Category	MainCategory::Primary Care Office
Sub Category	SubCategory::Cardiovascular
Prompt	[[Prompt::A 60 year-old female comes to your office complaining of fatigue, lethargy, intolerance of cold and dry skin. These symptoms started gradually over the last month. The patient has a past medical history of hypertension for 15 years which is controlled by metoprolol and hydrochlorothiazide, thyroiditis which was treated successfully with corticosteroids 3 years ago, and atrial fibrillation 1 year ago which is controlled by amiodarone and warfarin with controlled INR. On examination, all vital signs are normal, no pain or swelling in her neck. Serum TSH is elevated, with low levels of free T4. What is the most probable cause of hypothyroidism in this patient?]]
Answer A	AnswerA::Metoprolol
Answer A Explanation	[[AnswerAExp::Incorrect Amiodarone-induced hypothyroidism (AIH) is cause of this thyroid function abnormality.]]
Answer B	AnswerB::Warfarin
Answer B Explanation	[[AnswerBExp::Incorrect Amiodarone-induced hypothyroidism (AIH) is cause of this thyroid function abnormality.]]
Answer C	AnswerC::Inflammatory
Answer C Explanation	[[AnswerCExp::Incorrect There are no signs of inflammation in this patient. Amiodarone-induced hypothyroidism (AIH) is cause of this thyroid function abnormality.]]
Answer D	AnswerD::Anti arrhythmic medication
Answer D Explanation	[[AnswerDExp::Correct Amiodarone-induced hypothyroidism (AIH) is cause of this thyroid function abnormality.]]
Answer E	AnswerE::Hydrochlorothiazid
Answer E Explanation	[[AnswerEExp::Incorrect Amiodarone-induced hypothyroidism (AIH) is cause of this thyroid function abnormality.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::Amiodarone-induced hypothyroidism (AIH) is believed to result from the inability of the thyroid to escape from the Wolff-Chaikoff effect. Amiodarone is a benzofuranic-derivative iodine-rich drug, the large amount of iodide released during the metabolism of amiodarone leads to an adaptive blockage of further thyroidal iodide uptake and thyroid hormone biosynthesis, the so-called Wolff-Chaikoff effect. The reported incidence of AIH varies widely, ranging from 6% in countries with low iodine intake to 13% in countries with a high dietary iodine intake. The risk of developing hypothyroidism is independent of the daily or cumulative dose of amiodarone. However, the risk is greater in the elderly and in female patients, probably as a result of a higher prevalence of underlying thyroid abnormality. The relative risk of developing AIH was found to be 13-fold higher in female patients with positive thyroid microsomal or thyroglobulin antibodies, as compared with men without thyroid antibodies. Reference: "Effects of amiodarone on thyroid function.", journal = Ann Intern Med, volume = 126, issue = 1, month = Jan, year = 1997, PMID = 8992925. "Amiodarone and the thyroid: a practical guide to the management of thyroid dysfunction induced by amiodarone therapy.", journal = Heart, volume = 79, issue = 2, month = Feb, year = 1998, PMID = 9538302. "Incidence, predictability, and pathogenesis of amiodarone-induced thyrotoxicosis and hypothyroidism." journal = Am J Med, volume = 91, issue = 5, month = Nov, year = 1991, PMID = 1951413. Educational Objective: References: ]]
Approved	Approved::No
Keyword	[[WBRKeyword::Amiodarone]]
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Order in Linked Questions	LinkedOrder::