MD - Doctor of Medicine Endocrine and Metabolic Disorders Questions and Answers — Questions and Answers
Question 1: A 24-year-old female with a known history of type 1 diabetes presents to the emergency department with nausea, vomiting, abdominal pain, and deep, rapid breathing. Her blood glucose is 550 mg/dL, arterial pH is 7.15, and serum ketones are strongly positive. After confirming the diagnosis of Diabetic Ketoacidosis (DKA), what is the most critical initial step in management?
- Administer a subcutaneous dose of long-acting insulin.
- Begin intravenous regular insulin infusion.
- Start aggressive intravenous fluid resuscitation with normal saline. (Correct answer)
- Administer intravenous sodium bicarbonate to correct acidosis.
Correct answer: Start aggressive intravenous fluid resuscitation with normal saline.
The most critical initial step in managing DKA is aggressive intravenous fluid resuscitation. Patients with DKA are severely volume-depleted (often 5-10 liters). Restoring circulatory volume improves tissue perfusion, enhances renal function to help clear glucose and ketones, and lowers counter-regulatory hormones. While insulin is essential to stop ketogenesis, it should be started after initial fluid resuscitation has begun. Administering insulin without first giving fluids can worsen hypotension and lead to cardiovascular collapse as water shifts into cells along with glucose.
Question 2: A 42-year-old female presents with central obesity, purple striae, hypertension, and easy bruising. You suspect Cushing's syndrome. Which of the following is considered a first-line screening test to confirm hypercortisolism?
- Plasma ACTH level.
- High-dose dexamethasone suppression test.
- Abdominal MRI.
- 24-hour urinary free cortisol measurement. (Correct answer)
Correct answer: 24-hour urinary free cortisol measurement.
First-line screening tests for Cushing's syndrome aim to document endogenous hypercortisolism. The three accepted initial tests are the 24-hour urinary free cortisol (UFC), the late-night salivary cortisol, and the 1-mg overnight dexamethasone suppression test. A plasma ACTH level and a high-dose dexamethasone suppression test are second-line tests used to determine the *cause* of Cushing's syndrome (i.e., pituitary vs. adrenal vs. ectopic) after hypercortisolism has been confirmed. Imaging is performed only after biochemical confirmation.
Question 3: A 68-year-old male with small cell lung cancer is admitted with confusion and lethargy. His laboratory results are significant for a serum sodium of 118 mEq/L. Which of the following laboratory patterns is most consistent with the Syndrome of Inappropriate Antidiuretic Hormone (SIADH)?
- Euvolemic hyponatremia, high urine osmolality (>100 mOsm/kg), high urine sodium (>40 mEq/L). (Correct answer)
- Hypervolemic hyponatremia, low urine osmolality (<100 mOsm/kg), low urine sodium (<20 mEq/L).
- Hypovolemic hyponatremia, high urine osmolality (>450 mOsm/kg), low urine sodium (<20 mEq/L).
- Euvolemic hyponatremia, low urine osmolality (<100 mOsm/kg), high urine sodium (>40 mEq/L).
Correct answer: Euvolemic hyponatremia, high urine osmolality (>100 mOsm/kg), high urine sodium (>40 mEq/L).
The key features of SIADH are euvolemic hyponatremia due to excess free water retention. Despite the low serum osmolality, the urine is inappropriately concentrated (urine osmolality >100 mOsm/kg). The body attempts to excrete the excess fluid by promoting natriuresis, leading to a high urine sodium concentration (typically >40 mEq/L).
Question 4: A 35-year-old patient reports episodic headaches, palpitations, and profuse sweating, often accompanied by severe hypertension. A pheochromocytoma is suspected. What is the most appropriate initial biochemical test to establish the diagnosis?
- Serum epinephrine and norepinephrine levels.
- 24-hour urine for vanillylmandelic acid (VMA).
- Plasma free metanephrines. (Correct answer)
- Clonidine suppression test.
Correct answer: Plasma free metanephrines.
The initial and most sensitive biochemical test for diagnosing pheochromocytoma is the measurement of plasma free metanephrines or 24-hour urinary fractionated metanephrines. Catecholamines (epinephrine and norepinephrine) are released episodically and can have a short half-life, potentially leading to false-negative results if measured between spells. Metanephrines are metabolites of catecholamines and are produced continuously within the tumor, making them a more reliable marker.
Question 5: A patient with Graves' disease is started on methimazole. Which of the following best describes the primary mechanism of action of this thionamide medication?
- It blocks the peripheral conversion of T4 to T3.
- It inhibits the thyroid peroxidase enzyme, blocking the organification of iodine. (Correct answer)
- It competitively blocks the TSH receptor on thyroid follicular cells.
- It destroys thyroid follicular cells through radioactive emission.
Correct answer: It inhibits the thyroid peroxidase enzyme, blocking the organification of iodine.
Methimazole's primary mechanism of action is the inhibition of the thyroid peroxidase (TPO) enzyme. This enzyme is crucial for oxidizing iodide and coupling it to tyrosine residues on thyroglobulin (a process called organification), which is a critical step in the synthesis of thyroid hormones T3 and T4. Propylthiouracil (PTU) also inhibits TPO but has the additional effect of blocking the peripheral conversion of T4 to T3.
Question 6: A 60-year-old woman is found to have an elevated serum calcium level of 11.5 mg/dL on routine labs. A subsequent workup confirms primary hyperparathyroidism. Which of the following sets of laboratory findings is most characteristic of this condition?
- High serum calcium, high serum phosphate, low parathyroid hormone (PTH).
- High serum calcium, low serum phosphate, high or inappropriately normal parathyroid hormone (PTH). (Correct answer)
- Low serum calcium, high serum phosphate, high parathyroid hormone (PTH).
- High serum calcium, low serum phosphate, low parathyroid hormone (PTH).
Correct answer: High serum calcium, low serum phosphate, high or inappropriately normal parathyroid hormone (PTH).
In primary hyperparathyroidism, one or more parathyroid glands autonomously secrete excessive amounts of PTH. PTH acts to increase serum calcium (via bone resorption and renal reabsorption) and decrease serum phosphate (by increasing renal excretion). Therefore, the classic biochemical profile is hypercalcemia, hypophosphatemia, and an elevated or inappropriately normal PTH level (a normal PTH is inappropriate in the setting of hypercalcemia).
MD - Doctor of Medicine Endocrine and Metabolic Disorders Questions and Answers
A 24-year-old female with a known history of type 1 diabetes presents to the emergency department with nausea, vomiting, abdominal pain, and deep, rapid breathing.
Her blood glucose is 550 mg/dL, arterial pH is 7.15, and serum ketones are strongly positive.
After confirming the diagnosis of Diabetic Ketoacidosis (DKA), what is the most critical initial step in management?