USMLE Step 2 Quiz
Practice Thyroid And Calcium Disorders in USMLE Step 2 with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.
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A 72-year-old man is in the intensive care unit for severe pneumonia and septic shock. A set of thyroid function tests is ordered as part of a routine workup. The results are: TSH 0.6 µIU/mL (normal 0.4-4.0), free T4 0.8 ng/dL (normal 0.8-1.8), and total T3 40 ng/dL (normal 80-200). The patient has no prior history of thyroid disease.
What is the most appropriate next step in management?
This quiz focuses on Thyroid And Calcium Disorders, giving you a quick way to practice the rules, question types, and explanations that matter most for USMLE Step 2.
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A 72-year-old man is in the intensive care unit for severe pneumonia and septic shock. A set of thyroid function tests is ordered as part of a routine workup. The results are: TSH 0.6 µIU/mL (normal 0.4-4.0), free T4 0.8 ng/dL (normal 0.8-1.8), and total T3 40 ng/dL (normal 80-200). The patient has no prior history of thyroid disease.
What is the most appropriate next step in management?
Explanation: The laboratory pattern of low T3 with normal or low-normal T4 and TSH in a critically ill patient is characteristic of euthyroid sick syndrome (also known as non-thyroidal illness syndrome). This is an adaptive response to severe illness, primarily caused by decreased peripheral conversion of T4 to T3. Treatment with thyroid hormone is not indicated and may be harmful. The most appropriate course of action is to manage the underlying critical illness and re-evaluate thyroid function after the patient has recovered.
A 68-year-old woman presents for a follow-up appointment. Routine labs were drawn last week. She feels well and has no specific complaints. Her medical history is significant for hypertension. Labs show a TSH of 12.5 µIU/mL (reference range 0.4-4.0 µIU/mL) and a normal free T4 level. A repeat TSH level today is 11.8 µIU/mL.
Which of the following is the most appropriate next step?
Explanation: This patient has subclinical hypothyroidism, defined by an elevated TSH with a normal free T4 level. While treatment for mild elevations (TSH < 10 µIU/mL) is controversial, there is general consensus to treat when the TSH is persistently > 10 µIU/mL, as this is associated with an increased risk of progression to overt hypothyroidism and potential cardiovascular effects. Since her TSH is persistently above 10, initiating levothyroxine therapy is the most appropriate step.
A 33-year-old woman presents 5 months postpartum with palpitations, anxiety, and fatigue. She has a small, non-tender goiter. Laboratory tests reveal a TSH of 0.01 µIU/mL and an elevated free T4. A radioactive iodine uptake scan shows near-absent uptake (1% at 24 hours).
What is the most likely diagnosis?
Explanation: The combination of transient hyperthyroidism in the postpartum period with a non-tender goiter and a low radioactive iodine uptake is characteristic of postpartum thyroiditis. This condition is a form of destructive thyroiditis where preformed thyroid hormone is released from an inflamed gland. The low RAIU scan differentiates it from Graves' disease or a toxic adenoma, where uptake would be high. While factitious hyperthyroidism also causes low uptake, the presence of a goiter makes thyroiditis more likely.
A patient is being treated for hypocalcemic tetany secondary to iatrogenic hypoparathyroidism with intravenous calcium gluconate. Despite continuous infusion, her serum calcium level remains low, and she continues to have symptoms. Her serum magnesium level is 0.9 mg/dL (reference range 1.7-2.2 mg/dL).
What is the most appropriate next step in management?
Explanation: This patient has refractory hypocalcemia in the setting of significant hypomagnesemia. Magnesium is a crucial cofactor for both the secretion of PTH from the parathyroid glands and for PTH action on target tissues. Severe hypomagnesemia can cause functional hypoparathyroidism and end-organ resistance to PTH, leading to hypocalcemia that is refractory to calcium replacement alone. The hypocalcemia will not correct until the magnesium deficit is repleted. Therefore, administering intravenous magnesium sulfate is the most critical next step.
A 12-year-old boy is evaluated for short stature and dental abnormalities. Physical examination is notable for a round face, obesity, and shortened fourth and fifth metacarpals (brachydactyly). Laboratory results are as follows: Serum calcium: 7.8 mg/dL (low), Serum phosphorus: 5.8 mg/dL (high), Serum creatinine: 0.7 mg/dL (normal).
Which of the following additional laboratory findings is most likely to be found in this patient?
Explanation: The patient's phenotype (Albright hereditary osteodystrophy) combined with hypocalcemia and hyperphosphatemia is classic for pseudohypoparathyroidism type 1a. This is a genetic disorder characterized by end-organ resistance to parathyroid hormone (PTH). The kidneys and bones do not respond appropriately to PTH. In response to the persistent hypocalcemia, the parathyroid glands are appropriately stimulated and produce high amounts of PTH. Therefore, an elevated PTH level is expected, distinguishing this condition from true hypoparathyroidism where PTH would be low.
A 45-year-old man is evaluated for asymptomatic hypercalcemia discovered on routine labs. His serum calcium is 11.0 mg/dL and his PTH level is elevated. His father and paternal uncle also have a history of mild hypercalcemia. A 24-hour urine collection is ordered.
Which of the following results from the 24-hour urine collection would be most consistent with a diagnosis of familial hypocalciuric hypercalcemia (FHH)?
Explanation: Both primary hyperparathyroidism (PHPT) and familial hypocalciuric hypercalcemia (FHH) present with hypercalcemia and elevated or inappropriately normal PTH. The key differentiating feature is renal calcium handling. In PHPT, urinary calcium excretion is typically normal or high (>200 mg/24 hr). In FHH, a genetic disorder of the calcium-sensing receptor, the kidneys abnormally reabsorb calcium, leading to low urinary calcium excretion, typically <100 mg/24 hr. A calcium-to-creatinine clearance ratio <0.01 is also characteristic of FHH. The family history further supports FHH.
A 70-year-old man with a history of atrial fibrillation maintained on amiodarone for the last three years presents with new-onset anxiety and a 10-lb weight loss. His thyroid gland is non-tender. Labs reveal a TSH of <0.01 µIU/mL and a free T4 of 4.2 ng/dL. A color Doppler ultrasound of the thyroid is performed.
Which finding on the ultrasound would most strongly suggest amiodarone-induced thyrotoxicosis (AIT) Type 1?
Explanation: Amiodarone-induced thyrotoxicosis (AIT) has two main types. AIT Type 1 is an iodine-induced hyperthyroidism occurring in patients with pre-existing thyroid disease (e.g., latent Graves' or multinodular goiter). It is a state of true hormone overproduction, which is associated with increased blood flow (vascularity) on color Doppler ultrasound. AIT Type 2 is a destructive thyroiditis caused by a direct toxic effect of amiodarone, resulting in the release of preformed hormone and decreased vascularity. Therefore, increased vascularity points towards AIT Type 1.
A 35-year-old woman presents with palpitations and anxiety. She had an upper respiratory infection three weeks ago. On examination, her thyroid gland is exquisitely tender to palpation. Laboratory results show a TSH of 0.05 µIU/mL, elevated free T4, and an erythrocyte sedimentation rate (ESR) of 90 mm/hr.
What is the most appropriate initial treatment for this patient's condition?
Explanation: This patient's presentation of a painful thyroid gland, preceding viral illness, elevated inflammatory markers (ESR), and transient hyperthyroidism is classic for subacute (de Quervain's) thyroiditis. The hyperthyroidism is due to the release of preformed hormone from the inflamed, damaged gland, not due to new hormone synthesis. Therefore, antithyroid drugs like methimazole are ineffective. The mainstay of treatment is supportive care, focusing on pain and inflammation control with NSAIDs for mild to moderate cases, or corticosteroids for severe cases. The condition is self-limited.
A 71-year-old woman is evaluated for new-onset atrial fibrillation. She also reports a 3-month history of mild fatigue and weight loss. On examination, she has an irregularly irregular heart rate of 115/min and a moderately enlarged, nodular thyroid gland. Laboratory studies show a TSH of 0.03 µIU/mL and an elevated free T4.
Which of the following is the most likely finding on a technetium-99m pertechnetate thyroid scan?
Explanation: This patient's presentation of hyperthyroidism (suppressed TSH), atrial fibrillation, and a nodular goiter in an older adult is highly suggestive of toxic multinodular goiter (TMNG). In TMNG, multiple autonomous nodules develop that produce thyroid hormone independent of TSH stimulation. A thyroid scan will characteristically show multiple foci of increased radionuclide uptake corresponding to these hyperfunctioning nodules, with suppression of uptake in the normal surrounding thyroid tissue due to the low TSH level.