Hypothyroidism: Pathology review

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Hypothyroidism: Pathology review

Endocrine system


Hypothyroidism: Pathology review

USMLE® Step 1 questions

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USMLE® Step 1 style questions USMLE

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A 63-year-old man comes to the clinic for the first time complaining of excessive fatigue. He moved three months ago and is looking to establish care with a new physician. The patient states that he has felt tired and lethargic for the last 2 weeks. The patient is taking a medication for a “heart condition,” but he is unable to recall the name. He has also been taking acetaminophen daily to help relieve pain in his sore arms, which also started several weeks ago, and laxatives to help with bowel movements, which have slowed recently. Temperature is 37.2°C (99.0°F), pulse is 58/min and irregular, and blood pressure is 128/82 mm Hg. Physical examination reveals a slightly bluish hue to his skin. The upper extremities are diffusely tender to palpation. Laboratory studies are as follows:  
 Laboratory value  Result 
 Sodium  137 mEq/L 
 Potassium  4.8 mEq/L 
 Chloride  97 mEq/L 
 Glucose  97 mEq/L 
 Creatine kinase (CK)  145 U/L 
 Aspartate aminotransferase  66 U/L 
 Alanine aminotransferase  77 U/L 

Which of the following medications was this patient most likely taking?


On the Endocrinology ward, two individuals came in. The first one is 23 year old Hannah who complains of lethargy, fatigue, reduced appetite, muscle weakness and constipation. She also says that lately she gained a bit of weight and has a low libido. On clinical examination, she has periorbital edema, dry, cool skin, her nails are brittle and her reflexes are slow. She also has a moderately enlarged, painless goiter. The other one is 33 year old Quentin, who also presents with lethargy, fatigue, reduced appetite, muscle weakness, constipation and he’s also complaining about feeling cold all the time. He said that he recently had the flu, but no other illnesses. On clinical examination, there’s periorbital edema, dry, cool skin, brittle nails and hair, and a very painful goiter. TSH, free T3 and T4 are taken, along with antithyroid-peroxidase and antithyroglobulin antibodies. Both Hannah and Quentin have high levels of TSH and low T3 and T4 levels, but Hannah has positive antithyroid-peroxidase and antithyroglobulin antibodies.

Both individuals seem to have hypothyroidism. First, a bit of physiology. Normally, the hypothalamus detects low serum levels of thyroid hormones and releases thyrotropin-releasing hormone or TRH into the hypophyseal portal system. The anterior pituitary then releases thyroid-stimulating hormone, also called thyrotropin or simply TSH. TSH stimulates the thyroid gland. The thyroid gland is made up of thousands of follicles, which are small spheres lined with follicular cells. Follicular cells convert thyroglobulin, a protein found in follicles, into two iodine-containing hormones, triiodothyronine or T3, and thyroxine or T4. Once released from the thyroid gland, these hormones enter the blood and bind to circulating plasma proteins. Only a small amount of T3 and T4 will travel unbound in the blood, and can act upon nearly every type of cell in the body. Once inside the cell T­4 is usually converted into T3, and it can exert its effect. T3 speeds up the cell’s basal metabolic rate. It increases cardiac output, stimulates bone resorption, basically thinning out the bones, and activates the sympathetic nervous system. Thyroid hormones are also involved in a number of other things, like controlling sebaceous and sweat gland secretion, hair follicle growth, and regulating proteins and mucopolysaccharide synthesis by skin fibroblasts.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Riedel's Thyroiditis: A Clinical Review" The Journal of Clinical Endocrinology & Metabolism (2011)
  4. "The History and Future of Treatment of Hypothyroidism" Annals of Internal Medicine (2016)
  5. "Central Hypothyroidism: Pathogenic, Diagnostic, and Therapeutic Challenges" The Journal of Clinical Endocrinology & Metabolism (2012)
  6. "Hypothyroidism" Aust Fam Physician (2014)
  7. "Approach to the Patient with Postpartum Thyroiditis" The Journal of Clinical Endocrinology & Metabolism (2012)

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