Endocrinology Practice Questions

Q: A patient presents with symptoms of hypoglycemia. Investigations reveal decreased blood glucose and increased insulin levels. A C-peptide assay shows normal levels of C-peptide. What is the most likely diagnosis?

Accidental exogenous insulin administration. ### Explanation The key to solving this clinical scenario lies in understanding the synthesis of endogenous insulin. Insulin is synthesized as **proinsulin**, which is cleaved into equal molar amounts of **active insulin** and **C-peptide** before being released into the bloodstream. **1. Why Option C is Correct:** In **exogenous insulin administration**, the patient injects pre-formed, purified insulin. This commercial insulin does not contain C-peptide. Therefore, the patient will present with the biochemical triad of: * **Low Blood Glucose** (Hypoglycemia) [3] * **High Insulin** (Exogenous) * **Low/Normal C-peptide** (Endogenous production is actually suppressed due to negative feedback from hypoglycemia) [1]. **2. Why the other options are incorrect:** * **Insulinoma (A):** This is an insulin-secreting tumor of the pancreas. Since it produces endogenous insulin, both **Insulin and C-peptide levels will be elevated** [1]. * **Sulfonylurea Ingestion (B):** Sulfonylureas are secretagogues that stimulate the pancreas to release its own insulin [2]. Consequently, both **Insulin and C-peptide levels will be elevated**, mimicking an insulinoma [1]. * **Metformin Ingestion (D):** Metformin works by increasing insulin sensitivity and decreasing hepatic glucose production; it does not increase insulin secretion and typically does not cause hypoglycemia in isolation. **3. NEET-PG High-Yield Pearls:** * **Factitious Hypoglycemia:** Suspect this in healthcare workers or relatives of diabetics. [1] * **Differential Diagnosis:** To differentiate Insulinoma from Sulfonylurea abuse (as both have high C-peptide), a **Screening for Oral Hypoglycemic Agents** in the urine or plasma is required [1]. * **Whipple’s Triad:** 1. Symptoms of hypoglycemia, 2. Low plasma glucose, 3. Relief of symptoms after glucose administration. This triad confirms a hypoglycemic disorder.

Q: Hypocalcemia is seen with which of the following conditions?

Acute pancreatitis. Hypocalcemia is a classic metabolic complication of acute pancreatitis [2]. The primary mechanism is saponification: during pancreatic inflammation, released lipases break down peripancreatic fat into free fatty acids. These fatty acids bind to circulating ionized calcium, forming insoluble calcium soaps (salts) in the retroperitoneum. Additionally, a transient "parathyroid hormone (PTH) resistance" and hypomagnesemia may contribute to the decline in serum calcium levels [2]. In the Ranson Criteria, a fall in serum calcium (<8 mg/dL) within 48 hours is a marker of severe disease and poor prognosis. **Incorrect Options:** * **A. Thyrotoxicosis:** Excess thyroid hormone increases bone turnover by stimulating osteoclastic activity, which typically leads to **mild hypercalcemia** and hypercalciuria [1]. * **B. Hyperparathyroidism:** Primary hyperparathyroidism is characterized by the "classic triad" of **hypercalcemia**, hypophosphatemia, and elevated PTH [1]. * **D. Addison Disease:** Adrenal insufficiency is associated with **hypercalcemia** [1]. This occurs due to decreased renal calcium excretion and increased bone resorption, though the exact mechanism remains multifactorial. **High-Yield Clinical Pearls for NEET-PG:** * **Chvostek sign** (facial twitching on tapping the facial nerve) and **Trousseau sign** (carpal spasm on BP cuff inflation) are clinical markers of hypocalcemia. * **ECG finding:** The hallmark of hypocalcemia is **QT interval prolongation** (specifically the ST segment) [2]. * **Correction:** Always check serum albumin; for every 1 g/dL drop in albumin below 4 g/dL, add 0.8 mg/dL to the measured calcium to get the "corrected calcium" [2].

Q: A 36-year-old man presents with lethargy, weakness, and confusion. His serum sodium and serum osmolality are markedly decreased, while urine osmolality is increased. These findings are most likely related to which of the following?

Small cell carcinoma of the lung. **Explanation:** The clinical presentation of lethargy, confusion, and laboratory findings of **hyponatremia** (low serum sodium), **low serum osmolality**, and **concentrated urine** (high urine osmolality) is a classic description of the **Syndrome of Inappropriate Antidiuretic Hormone (SIADH)** [1]. **Why Small Cell Carcinoma of the Lung (SCLC) is Correct:** SCLC is the most common malignancy associated with SIADH [3], [4]. It is a neuroendocrine tumor that frequently exhibits **paraneoplastic syndromes** by ectopically secreting ADH (Arginine Vasopressin) [3]. Excess ADH causes water reabsorption in the renal collecting ducts via V2 receptors and aquaporin channels, leading to dilutional hyponatremia and inappropriately concentrated urine despite low plasma osmolality [2]. **Analysis of Incorrect Options:** * **Bronchogenic Carcinoma (Option A):** While this is a broad term, it usually refers to Non-Small Cell Lung Cancer (NSCLC). Squamous cell carcinoma is classically associated with hypercalcemia (PTHrP), not SIADH [3]. * **Thymoma (Option B):** Thymomas are most commonly associated with Myasthenia Gravis, Pure Red Cell Aplasia, and Hypogammaglobulinemia (Good Syndrome). * **Renal Cell Carcinoma (Option D):** RCC is known for paraneoplastic syndromes like erythrocytosis (EPO production), hypercalcemia (PTHrP), and Stauffer syndrome, but it is not a classic cause of SIADH [3]. **High-Yield Clinical Pearls for NEET-PG:** * **SIADH Criteria:** Euvolemic hyponatremia, Urine Osmolality >100 mOsm/kg, and Urine Sodium >40 mEq/L [1]. * **Drug Causes:** Carbamazepine, Cyclophosphamide, and SSRIs are frequent triggers. * **Management:** Fluid restriction is the first-line treatment. For severe/symptomatic hyponatremia, use 3% hypertonic saline. * **Caution:** Rapid correction of hyponatremia can lead to **Osmotic Demyelination Syndrome** (Central Pontine Myelinolysis).

Q: What is the test of choice for diagnosing Cushing's syndrome?

Overnight low dose Dexamethasone suppression test. To diagnose Cushing’s syndrome, clinicians must follow a two-step process: **Screening** (to confirm hypercortisolism) and **Localization** (to find the source) [1]. ### Why Option B is Correct The **Overnight Low-Dose Dexamethasone Suppression Test (ONDST)** is a primary screening test. In healthy individuals, 1 mg of dexamethasone at 11 PM suppresses ACTH, leading to a morning cortisol level of **<1.8 µg/dL** [1]. Patients with Cushing’s syndrome lack this negative feedback mechanism and fail to suppress cortisol. Other valid screening tests include 24-hour urinary free cortisol and late-night salivary cortisol [1]. ### Why Other Options are Incorrect * **Option A (High-Dose DST):** This is a **localization test**, not a screening test. It is used to differentiate between Pituitary Cushing’s (which suppresses by >50%) and Ectopic ACTH production (which does not suppress). * **Option B (CRH Test):** This is used for differential diagnosis (localization) after hypercortisolism is confirmed, helping distinguish between Cushing’s disease and ectopic sources. * **Option D (Insulin Tolerance Test):** While once a gold standard for assessing the HPA axis, it is rarely used for Cushing's diagnosis due to safety risks (hypoglycemia) and is more relevant for diagnosing Growth Hormone deficiency or adrenal insufficiency. ### NEET-PG High-Yield Pearls * **Best Initial Screening Test:** ONDST or Late-night salivary cortisol [1]. * **Gold Standard for Localization:** Inferior Petrosal Sinus Sampling (IPSS) is the most accurate way to confirm a pituitary source versus an ectopic source. * **Pseudo-Cushing’s:** Conditions like depression, alcoholism, and obesity can cause false positives in screening tests. * **Drug Interference:** Phenytoin and Rifampin increase dexamethasone metabolism, potentially causing false-positive ONDST results.

Q: A patient with diabetic nephropathy developed secondary hyperparathyroidism. Hyperparathyroidism is seen in all of the following conditions, EXCEPT:

Osteoporosis. **Explanation:** The core concept behind this question is the distinction between **metabolic bone diseases** that affect bone quality versus those that trigger a compensatory hormonal response. **Why Osteoporosis is the Correct Answer:** Osteoporosis is characterized by a decrease in **total bone mass** (both mineral and matrix are lost), but the remaining bone is biochemically normal. Crucially, serum levels of Calcium, Phosphate, and **Parathyroid Hormone (PTH) remain normal** in primary osteoporosis. There is no physiological trigger for hyperparathyroidism because there is no underlying vitamin D deficiency or hypocalcemia. **Analysis of Incorrect Options:** * **Chronic Renal Failure (CRF):** This is the classic cause of **Secondary Hyperparathyroidism**. In CRF, the kidneys fail to convert Vitamin D to its active form (1,25-OH₂D) and fail to excrete phosphate [1], [2]. The resulting hypocalcemia and hyperphosphatemia stimulate the parathyroid glands to overproduce PTH (Renal Osteodystrophy) [3]. * **Rickets (Children) and Osteomalacia (Adults):** Both conditions involve defective mineralization of the bone matrix, usually due to **Vitamin D deficiency** [2]. Low Vitamin D leads to decreased intestinal calcium absorption. The resulting hypocalcemia triggers a compensatory increase in PTH (Secondary Hyperparathyroidism) to maintain serum calcium levels [1]. **NEET-PG High-Yield Pearls:** 1. **Biochemical Profile of Osteoporosis:** Normal Ca²ⁱ, Normal PO₄³⁻, Normal ALP, Normal PTH. 2. **Secondary Hyperparathyroidism:** Characterized by **Low/Normal Calcium** and **High PTH** [2]. 3. **Tertiary Hyperparathyroidism:** Seen in long-standing CRF where the parathyroid glands become autonomous, leading to **High Calcium** and **Very High PTH** [3]. 4. **Hungry Bone Syndrome:** A common post-parathyroidectomy complication where sudden PTH withdrawal causes rapid calcium uptake by bones, leading to severe hypocalcemia.

Question 1

A patient presents with symptoms of hypoglycemia. Investigations reveal decreased blood glucose and increased insulin levels. A C-peptide assay shows normal levels of C-peptide. What is the most likely diagnosis?

Accepted Answer

Accidental exogenous insulin administration

Answer

Insulinoma

Answer

Accidental sulfonylurea ingestion

Answer

Accidental metformin ingestion

Question 2

Hypocalcemia is seen with which of the following conditions?

Accepted Answer

Acute pancreatitis

Answer

Thyrotoxicosis

Answer

Hyperparathyroidism

Answer

Addison disease

Question 3

A 29-year-old individual, a known diabetic on oral hypoglycemic agents for 3 years, has experienced weight loss and has never had diabetic ketoacidosis. Both his paternal grandfather and father are diabetic. Which of the following is the most likely diagnosis?

Accepted Answer

Maturity-onset diabetes of the young (MODY)

Answer

Type 1 Diabetes Mellitus

Answer

Type 2 Diabetes Mellitus

Answer

Pancreatic diabetes

Question 4

What is the most reliable test in the diagnosis of pheochromocytoma?

Accepted Answer

24-hour urinary metanephrine

Answer

Urinary catecholamines

Answer

Plasma catecholamines

Answer

Basal plasma catecholamines

Question 5

A 36-year-old man presents with lethargy, weakness, and confusion. His serum sodium and serum osmolality are markedly decreased, while urine osmolality is increased. These findings are most likely related to which of the following?

Accepted Answer

Small cell carcinoma of the lung

Answer

Bronchogenic carcinoma

Answer

Thymoma

Answer

Renal cell carcinoma

Question 6

What is the test of choice for diagnosing Cushing's syndrome?

Accepted Answer

Overnight low dose Dexamethasone suppression test

Answer

High dose Dexamethasone suppression test

Answer

Corticotropin releasing hormone test

Answer

Insulin tolerance test

Question 7

A patient with diabetic nephropathy developed secondary hyperparathyroidism. Hyperparathyroidism is seen in all of the following conditions, EXCEPT:

Accepted Answer

Osteoporosis

Answer

Osteomalacia

Answer

Rickets

Answer

Chronic renal failure

Question 8

Pseudohypoparathyroidism is characterized by which of the following laboratory findings?

Accepted Answer

Decreased serum calcium and increased serum parathyroid hormone

Answer

Normal serum calcium and decreased serum parathyroid hormone

Answer

Decreased serum calcium and decreased serum parathyroid hormone

Answer

Normal serum calcium and increased serum parathyroid hormone

Question 9

A 45-year-old woman presents with sudden attacks of wheezing, shortness of breath, episodic hot flashes, abdominal cramps, and diarrhea. Physical examination shows facial redness, as well as hepatomegaly and pitting edema of the lower legs. A 24-hour urine specimen reveals elevated levels of 5-hydroxyindoleacetic acid (5-HIAA). A CT scan of the abdomen demonstrates multiple 2- to 3-cm nodules throughout the liver and a 2-cm nodule in the jejunum. An echocardiogram would be most expected to demonstrate which of the following?

Accepted Answer

Pulmonic stenosis

Answer

Aortic stenosis

Answer

Bacterial endocarditis

Answer

Mitral valve prolapse

Question 10

A 34-year-old man is referred for evaluation of hypertension and persistent hypokalemia in spite of taking oral potassium supplements. His blood pressure is 180/110 mm Hg. Serum sodium is 149 mEq/L; potassium, 3.3 mEq/L; bicarbonate, 29 mEq/L; chloride, 103 mEq/L; and blood urea nitrogen, 23 mg/dL. Computed tomography demonstrates a 3-cm mass in the right adrenal gland. The most likely diagnosis is:

Accepted Answer

Conn syndrome

Answer

Addison disease

Answer

Cushing syndrome

Answer

Sipple syndrome

Endocrinology — MCQs

Endocrinology — MCQs

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