ITE Endocrinology and Metabolism 4 — Questions and Answers
Question 1: A 30-year-old man presents with polyuria, polydipsia, and a serum sodium of 148 mEq/L. Urine osmolality is 110 mOsm/kg after water deprivation, rising to 680 mOsm/kg after desmopressin (DDAVP). What is the diagnosis?
- Nephrogenic diabetes insipidus
- Central (neurogenic) diabetes insipidus (Correct answer)
- Primary polydipsia
- Syndrome of inappropriate ADH
Correct answer: Central (neurogenic) diabetes insipidus
A markedly concentrated urine response to exogenous DDAVP after failure to concentrate with water deprivation indicates central diabetes insipidus, where ADH is deficient but the kidney can respond normally.
Question 2: A 58-year-old woman on long-term lithium therapy presents with fatigue and a calcium of 10.8 mg/dL. PTH is 72 pg/mL (high-normal). What is the most likely mechanism of her hypercalcemia?
- Lithium-induced autonomous parathyroid adenoma
- Lithium raises the calcium set-point for PTH suppression (Correct answer)
- Lithium causes vitamin D toxicity
- Lithium induces ectopic PTH production
Correct answer: Lithium raises the calcium set-point for PTH suppression
Lithium elevates the calcium threshold for PTH suppression (shifts the set-point), resulting in inappropriately elevated PTH and mild hypercalcemia; this is usually reversible upon lithium discontinuation.
Question 3: A 26-year-old woman with type 1 diabetes presents with recurrent DKA episodes despite good outpatient compliance. She has celiac antibodies positive on screening. How does undiagnosed celiac disease contribute to DKA in type 1 diabetes?
- Celiac disease causes insulin resistance
- Malabsorption leads to unpredictable glucose-insulin matching (Correct answer)
- Celiac increases glucagon secretion
- Celiac destroys beta cells directly
Correct answer: Malabsorption leads to unpredictable glucose-insulin matching
Celiac disease-related malabsorption causes erratic carbohydrate absorption, making glucose-insulin matching unpredictable and precipitating hypoglycemia or hyperglycemia and DKA.
Question 4: A 65-year-old man with metastatic lung cancer develops calcium of 13.5 mg/dL, low PTH, low 1,25-dihydroxyvitamin D, and elevated PTHrP. Which mechanism best explains his hypercalcemia?
- Local osteolytic metastases releasing calcium
- Humoral hypercalcemia of malignancy via PTHrP (Correct answer)
- Ectopic 1-alpha hydroxylase activity
- Adrenal insufficiency from metastases
Correct answer: Humoral hypercalcemia of malignancy via PTHrP
Elevated PTHrP with suppressed PTH and low 1,25-(OH)2D is the hallmark of humoral hypercalcemia of malignancy, the most common cause of cancer-related hypercalcemia.
Question 5: A 40-year-old woman has an incidentally discovered 2.5 cm adrenal mass on CT for kidney stones. She has no hypertension or symptoms. Hormonal workup shows: normal aldosterone/renin ratio, normal 24-hour urine catecholamines, and 1 mg overnight dexamethasone suppression test shows cortisol of 3.8 mcg/dL. What is the next step?
- Adrenalectomy
- Repeat imaging in 6–12 months and reassay hormones annually (Correct answer)
- PET scan to rule out malignancy
- Salivary cortisol testing
Correct answer: Repeat imaging in 6–12 months and reassay hormones annually
An adrenal incidentaloma <4 cm that is hormonally inactive (cortisol suppresses to <5 mcg/dL on 1 mg DST) should be followed with repeat imaging at 6–12 months and annual hormonal reassessment per guidelines.
Question 6: A 22-year-old woman with Turner syndrome (45,X) presents for routine evaluation. Which endocrine complication is she at highest risk for?
- Cushing syndrome
- Primary hyperparathyroidism
- Primary hypothyroidism (Hashimoto's) (Correct answer)
- Prolactinoma
Correct answer: Primary hypothyroidism (Hashimoto's)
Women with Turner syndrome have a significantly increased prevalence of autoimmune thyroid disease, particularly Hashimoto's thyroiditis and primary hypothyroidism.
Question 7: A 55-year-old man has low serum testosterone (180 ng/dL), LH 0.8 mIU/mL (low), and FSH 1.0 mIU/mL (low). MRI pituitary is normal. He takes opioids chronically for back pain. What is the diagnosis?
- Primary hypogonadism
- Opioid-induced hypogonadotropic hypogonadism (Correct answer)
- Klinefelter syndrome
- Idiopathic hypogonadotropic hypogonadism
Correct answer: Opioid-induced hypogonadotropic hypogonadism
Chronic opioid use suppresses GnRH pulsatility, reducing LH and FSH secretion and resulting in secondary (hypogonadotropic) hypogonadism with low testosterone.
ITE Endocrinology and Metabolism 4
A 30-year-old man presents with polyuria, polydipsia, and a serum sodium of 148 mEq/L.
Urine osmolality is 110 mOsm/kg after water deprivation, rising to 680 mOsm/kg after desmopressin (DDAVP).
What is the diagnosis?