10 USMLE Endocrinology Questions with Answers and Explanations (Set 1)

These 10 USMLE endocrinology practice questions cover thyroid, parathyroid, adrenal, pituitary and puberty topics that come up again and again on Step 1 and Step 2 CK. Each question includes the correct answer and an explanation.

Written by Dr. Ray Makar, MD, author of the Repeated USMLE Questions eBook series.

Prefer video? Watch daily USMLE case questions on MedFocus by Dr. Ray on YouTube.

How to use this page: read the question, pick your answer, then tap Show Answer and Explanation.

Questions

Question 1. A 30-year-old woman with a history of Graves disease presents to her physician for a routine evaluation. She was treated 2 years ago with radioactive iodine. Three months later, she was prescribed levothyroxine 0.125 mg. On her last evaluation, six months ago, her doctor lowered her dose to 0.088 mg due to decrease of TSH level. Today, her lab tests show an increase in T4 and T3 and very low TSH and positive TSH receptor antibodies. What is the most likely diagnosis?

A- Hashimoto’s disease
B- Radiation-induced thyroiditis
C- Ectopic thyroid tissue
D- Incomplete ablation of thyroid gland
E- Cancer thyroid

This is a typical presentation of incomplete ablation of thyroid gland. The patient went through radioactive ablation of her thyroid gland 2 years ago. In some cases, there is some thyroid tissue could be left after radiotherapy and starts to grow in size until becomes able to cause hyperthyroidism in addition to the use of levothyroxine treatment.
The correct answer is D

 

Question 2. A 28-year-old woman visits her physician complaining of fatigue, palpitations, loss of weight, diarrhea and irritability for 4 months. She is also intolerant to hot weather. She does not smoke or drink coffee or alcohol. Her vital signs are within normal limits except for rapid regular pulse. She has fine tremors and her skin is warm and moist. Her thyroid gland is asymmetrically enlarged and lobulated. Laboratory tests show: Thyroid stimulating hormone (TSH) 0.02 mu/ml and T4 28 mu/dL Her physician discusses advantages and disadvantages of all treatment options with the patient. What is the most important disadvantage of radioactive iodine therapy?

A- Anemia and agranulocytosis
B- Leukemia
C- Ablation of the gland and future hypothyroidism
D- Repeated doses due to repeated failures
E- Acute renal failure

Radioactive iodine therapy is the treatment of choice for hyperthyroidism with complications. It leads to ablation of the gland and future hypothyroidism. Patients should be informed before starting treatment of radioactive iodine therapy about the possibility of receiving long life treatment of levothyroxine.
The correct answer is C

 

Question 3. A 33-year-old man presents to his physician to discuss his plans for treatment of hyperthyroidism. One of the options is potassium perchlorate. What is the mechanism of action of potassium perchlorate as anti-thyroid?

A- Blocking of coupling of iodotyrosines
B- Blocking of peroxidase catalyzed reactions
C- Blocking of peripheral deiodination of T3 and T4
D- Competitive inhibition of iodide transport mechanism
E- Inhibition of the release of thyroid hormone from the thyroid gland

Potassium perchlorate prevents the uptake of iodine by thyroid gland by competitive inhibition of iodide transport mechanism.
The correct answer is D

 

Question 4. A 40 year-old woman presents to her regular physician for evaluation of a left adrenal mass. This mass was seen by accident last week on a CT scan during a visit to the emergency room for abdominal pain. Her vital signs, physical examination and review of systems are all normal. Her past history and family history are unremarkable. What is the first step in management for this patient?

A- Assure the patient and schedule another CT scan after 6 months
B- Order hormonal assay to evaluate if the mass is functional or not
C- Order MRI of the mass
D- Perform a needle biopsy
E- Refer to surgery for removal of the adrenal mass

This is a case of incidentaloma, as its name implies, a tumor that is discovered incidentally. The first crucial step is to find out if it is functional or not. Hormonal assay is the most appropriate method to figure that out.
The correct answer is B

 

Question 5. A 37-year-old woman presents to the emergency room complaining of general tingling sensation all over her body and spasm of her right hand for 1 hour. Her spasm is worsening and she feels as her body becomes more rigid. She had undergone subtotal thyroidectomy 2 weeks ago and the incision is healed and clean. Blood tests reveal very low serum calcium level. What should be the immediate therapy to reverse her symptoms?

A- Vitamin D
B- Calcitonin
C- Calcium gluconate
D- Levothyroxine
E- Parathyroid hormone

Low levels of parathyroid hormone (PTH) occur due to loss of parathyroid glands during thyroid surgeries. This condition leads to low calcium and high phosphorus serum levels. IV Calcium gluconate is the treatment of choice for severe hypocalcemia. Long term treatment with vitamin D and parathyroid hormone should be initiated as soon as diagnosis is confirmed.
The correct answer is C

 

Question 6. A 22-year-old man presents to the clinic due to excessive urination. He goes to the restroom almost every 15 minutes. His physical examination is otherwise normal. Laboratory tests show Serum Na: 140 mEq/L Urine output: 4 L/24 hours Urine is negative for glucose and protein and no pus cells Urine Na: 18 mEq/L Urine osmolality: 260 mOsm/kg after 4h fluid deprivation. What is the most likely diagnosis?

A- Diabetes mellitus
B- Diabetes insipidus
C- Psychogenic polydipsia
D- Urinary tract infection
E- Solute diuresis

The water deprivation test shows urine osmolality lower than 400 mOsm/kg, which is diagnostic for diabetes insipidus. It is >800 in normal person and >500 in polydipsia. Absence of glucose and pus in urine excludes DM and UTI respectively.
The correct answer is B

 

Question 7. A 46-year-old woman with a history of fibromyalgia presents to the clinic with a complaint of anxiety, frequent diarrhea and occasional palpitations. She also noticed an unexplained loss of weight and irregular menstrual periods over the last 3 months. What is the most likely laboratory investigation that could lead to a diagnosis in this case?

A- CT scan of the head
B- MRI of the brain
C- Colonoscopy
D- Cosyntropin stimulation test
E- Serum Thyroid Stimulation Hormone (TSH) level

This is most likely a case of Graves’ disease. It is an autoimmune disease characterized by the presence of antibodies bind to thyroid-stimulating hormone receptors. They lead to excess thyroid hormone production which results on this patient’s symptoms such as anxiety, diarrhea, arrhythmias, and unexplained loss of weight, heat intolerance and irregular menstrual periods. If serum TSH level is normal then, other tests can be done to exclude other conditions such as pituitary adenoma or GIT abnormalities.
The correct answer is E

 

Question 8. A concerned mother has brought her 8-year old girl to the gynecology clinic because of enlarged breasts. Her daughter has been feeling depressed as her schoolmates make fun of her for her large breasts. There is no axillary or pubic hair. There is no history of menarche. Her voice did not change. Her examination is completely normal. What is the most likely diagnosis?

A- Precocious puberty
B- Isolated premature thelarche
C- Pituitary adenoma
D- Androgen insensitivity syndrome
E- Congenital adrenal hyperplasia

This is a typical case of isolated premature thelarche. Precocious puberty is incorrect as it is characterized by premature menstruation and appearance of pubic and axillary hair in addition to enlarged breasts. It is a normal condition occurs in 40% of girls under the age of 8. There is no other symptoms suggesting any abnormality so, other options are all incorrect.
The correct answer is B

 

Question 9. A 17-year-old girl visits the clinic with her mother who is concerned that her daughter had not menstruated yet and her breast had not been significantly developed. She also notes that her daughter is color blind. The girl denies any sexual relationship or using any recreational drugs. Examination reveals normally appearing girl with small non-developed breasts. There is lack of pubic hair and her vagina and cervix are not fully developed. She is 5 feet 5 inches tall and weighs 130 lb. Cardiac, chest and abdominal examinations are unremarkable. What is the most likely initial diagnosis?

A- Androgen insensitivity disorder
B- Early pregnancy
C- Kallmann’s syndrome
D- Kartagener’s syndrome
E- Turner’s syndrome

This patient has primary amenorrhea, delayed secondary sexual development and color blindness. All these features are characteristic of Kallmann’s syndrome. It is a hereditary disorder of GnRH synthesis. Androgen sensitivity disorder is characterized by the development of breasts and female external genitalia in an XY candidate. This patient has primary amenorrhea and under-developed secondary sexual characteristics which exclude pregnancy. Kartagener’s syndrome characterized by recurrent respiratory tract infections due to lack of cilia and infertility in men due to defective sperm movement. Turner’s syndrome is characterized by amenorrhea and lack of secondary sexual characteristics. It is excluded in this case because it causes dysmorphic body shape and short stature which are not available in this case.
The correct answer is C

 

Question 10. A 5-year-old girl with a mass in her neck is brought to the clinic for an evaluation. Her mother says that this mass appeared 6 months ago and is increasing in size. There is no pain or discomfort. On examination, the mass is in the midline, inferior to the hyoid bone. Laboratory tests reveal normal thyroid panel. Surgery is recommended after a CT scan is performed. What is the most likely diagnosis?

A- Dermoid cyst
B- Ectopic thyroid gland
C- Lipoma
D- Thyroglossal duct cyst
E- Branchial cleft cyst

Normally, thyroglossal cyst disappears during development of the thyroid gland. In some cases, the duct remains in the neck and forms a cyst. It appears in the midline of the neck and is painless. Surgery is recommended to prevent infection if the CT scan shows a normal thyroid gland and thyroglossal duct cyst attached to it. All other options are possible causes but they are less common than thyroglossal duct cyst.
The correct answer is D

 

High-yield points from this set

  • Recurrent hyperthyroidism with TSH-receptor antibodies after radioactive iodine = incomplete ablation.
  • The main drawback of radioactive iodine is permanent hypothyroidism.
  • Perchlorate competitively blocks iodide uptake (the Na+/I− symporter).
  • Every adrenal incidentaloma first needs a hormonal work-up to see if it is functional.
  • Tetany after thyroid surgery = hypoparathyroidism; give IV calcium gluconate.
  • Urine that stays dilute after water deprivation = diabetes insipidus.
  • Anxiety, weight loss, diarrhea and palpitations: start with a serum TSH.
  • Breast development alone in a young girl, without pubic hair or growth spurt = isolated premature thelarche.
  • Primary amenorrhea, no breast development and normal height (with anosmia or color blindness) = Kallmann syndrome.
  • A painless midline neck mass below the hyoid in a child = thyroglossal duct cyst.

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