USMLE Step 1 Thyroid Disorders practice questions
Thyroid disorders are a high-yield endocrine topic on Step 1 spanning autoimmune disease (Graves disease, Hashimoto thyroiditis), neoplasia (papillary and medullary carcinoma), and the physiology of the hypothalamic-pituitary-thyroid axis. Step 1 tests the mechanisms behind thyroid dysfunction—autoantibody targets, enzyme defects, cell of origin, and feedback-loop logic—rather than treatment selection. Mastery requires linking a clinical picture (goiter character, TSH/T4 pattern, histology) back to the underlying molecular or cellular process.
A 32-year-old woman comes to the office because of a 3-month history of weight loss despite increased appetite, heat intolerance, and palpitations. She says her family has commented that her eyes look more prominent. Her pulse is 112/min and irregularly irregular. Examination shows a diffusely enlarged, non-tender thyroid gland with an audible bruit, fine hand tremor, and bilateral exophthalmos. Serum TSH is undetectable and free T4 is elevated. Which of the following is the most likely mechanism underlying this patient's thyroid findings?
Patient Information Age: 45 years | Gender: F, self-identified | Race/Ethnicity: White, self-identified | Site of Care: outpatient clinic History Reason for Visit/Chief Concern: "I've been so tired, and I've gained weight without trying." History of Present Illness: • 6-month history of fatigue, cold intolerance, and constipation • Unintentional 8-lb (3.6-kg) weight gain • No neck pain or tenderness Physical Examination Pulse: 58/min | BP: 118/76 mm Hg Thyroid gland diffusely enlarged, firm, non-tender, without discrete nodules Diagnostic Studies TSH: 18 µU/mL (0.4–4.0 µU/mL) Free T4: low Anti-thyroid peroxidase antibody titer: markedly elevated Which of the following is the most likely mechanism responsible for this patient's thyroid gland findings?
A 58-year-old woman comes to the office with fatigue, cold intolerance, and irregular menses that have developed over the past 4 months. She was diagnosed with a pituitary macroadenoma 6 months ago. Serum TSH is 0.3 µU/mL (0.4–4.0 µU/mL) and free T4 is low. A cosyntropin stimulation test is normal. Which of the following processes is most directly impaired in this patient?
A 38-year-old man comes to the office because of a firm, painless thyroid nodule found on routine examination. He reports episodic flushing and diarrhea over the past year. His mother died of pheochromocytoma, and a maternal uncle had a similar thyroid nodule. Serum calcitonin is markedly elevated. Biopsy of the nodule shows sheets of polygonal cells with amyloid deposits in the surrounding stroma. Which of the following is the most likely cell of origin of this tumor?
Patient Information Age: 29 years | Gender: F, self-identified | Site of Care: outpatient clinic (pregnant, 14 weeks gestation) History Reason for Visit/Chief Concern: "My heart feels like it's racing and I can't tolerate the heat." History of Present Illness: Diagnosed with Graves disease at 10 weeks gestation; started on an antithyroid medication that inhibits oxidation and organification of iodide and coupling of iodotyrosine residues. Physical Examination Pulse: 104/min Fine hand tremor, mild lid lag Which of the following enzymes is most likely inhibited by this patient's medication?
Thyroid Disorders, answered
What's the fastest way to distinguish Graves disease from Hashimoto thyroiditis on Step 1?
Look at the TSH/T4 pattern first: Graves causes hyperthyroidism (low TSH, high T4) from TSH-receptor-stimulating antibodies, while Hashimoto causes hypothyroidism (high TSH, low T4) from antibody- and T-cell-mediated follicular destruction. Exophthalmos and pretibial myxedema point specifically to Graves, since they result from orbital and dermal fibroblast stimulation that Hashimoto does not cause.
Do I need to memorize every adverse effect of methimazole and propylthiouracil for Step 1?
No—Step 1 emphasizes mechanism of action (thyroid peroxidase inhibition) over exhaustive adverse effect lists. It's still worth knowing the classic, testable associations: methimazole's teratogenicity (favoring propylthiouracil in the first trimester) and both drugs' rare risk of agranulocytosis, since these connect mechanism to a recognizable clinical vignette.
How do I tell primary from central (secondary) hypothyroidism using labs alone?
In primary hypothyroidism the thyroid gland itself fails, so TSH rises appropriately as the pituitary tries to compensate for a low T4. In central hypothyroidism the pituitary or hypothalamus fails to drive the thyroid, so TSH is low or inappropriately normal despite a low T4. A low TSH with a low T4 should make you think of a pituitary or hypothalamic problem, not primary thyroid failure.
Which thyroid cancers are considered must-knows, and how are they told apart histologically?
Papillary carcinoma (the most common type) shows Orphan Annie eye nuclei and psammoma bodies; follicular carcinoma shows capsular or vascular invasion on a background of follicular architecture; medullary carcinoma arises from calcitonin-secreting parafollicular C cells with amyloid stroma and is linked to MEN2; and anaplastic carcinoma is a highly aggressive, undifferentiated tumor of older adults. Knowing the cell of origin for each helps predict its associated hormone and clinical behavior.
Want unlimited Thyroid Disorders questions from your own notes?
Upload your lecture notes and QuizMed writes USMLE Step 1-style MCQs tuned to your material, free for your first five quizzes.
No credit card required.