14_HST110 Regulation of Calcium and Phosphorus 2017 Part 2

Question 1

80-90% of cases of Hypercalcemia are attributed to (X) and (Y)

Answer 1

X = malignancy
Y = hyperparathyroidism

Question 2

What is the mnemonic used to remember the clinical presentation of hypercalcemia?

Answer 2

Stones (kidney stones, polyuria), groans (confusion, dementia), moans (abdominal pain, nausea), and bones (bone pain, fractures)

Question 3

What is the #1 cause of hypercalcemia?

Answer 3

Increased secretion of PTH (primary hyperthyroidism) caused 85% of the time by parathyroid adenomas

Question 4

Hyperparathyroidism (increased PTH) effects of bone, and kidney

Answer 4

Bone: Increased resorption -> release of Ca2+ & Pi

Kidney: Increased Pi excretion, Increased Ca2+ reabsorption, Increased Calcitrol production -> Increased intestinal CaHPO4 absorption

CONSEQUENCE: High Plasma [Ca2+] and Low Plasma [Pi]

Question 5

What condition is characterized by the following features?

• Benign cause of hypercalcemia
• Family history of mild hypercalcemia and low urine calcium (<200 mg/d)
• Autosomal dominant inactivating mutations in the calcium-sensing receptor (CaSR)
• Patients usually asymptomatic
• Urine calcium/creatinine clearance <0.020

Answer 5

Familial Hypocalciuric Hypercalcemia

Question 6

Calcium Sensing Receptor (CaSR)

Expressed in multiple tissues, e.g. (X)

Regulates Ca2+ balance by sensing small changes in serum [Ca2+] and modulating (Y) release accordingly

⬆ sensed [Ca2+]
Inhibits (Y) secretion
Decreases renal Ca2+ reabsorption, and vice versa

Answer 6

X = Parathyroid glands, kidneys, bone, breast
Y = PTH

Question 7

Familial Hypocalciuric Hypercalcemia

Parathyroid gland

• *Less sensitive to (X)
• *Higher than normal serum [X] is required to suppress PTH
• *PTH levels are inappropriately (Y)

Kidney
Increase in (X) and (Z) reabsorption

NET EFFECTS:
(A)

Answer 7

X = Ca2+
Y = normal to high
Z = Mg2+
A = Hypercalcemia and Hypocalciuria

Question 8

How would you distinguish between primary hyperparathyroidism and familial hypocalciuric hypercalcemia in a patient with hypercalemia?

Answer 8

PTH is higher in Primary hyperthyroidism

Family history

Urine Calcium: High in Primary hyperthyroidism

Question 9

What condition is characterized by the following features?

Severe hypophosphatemia with osteomalacia that occurs as an acquired disorder associated with a tumor

Typically from small, benign, mesenchymal tumors

Tumor extracts inhibit phosphate transport in renal epithelial cells and produce hypophosphatemia and decrease calcitriol production in experimental animals

SERUM FGF-23 abnormally high

Answer 9

Osteogenic Osteomalacia

Question 10

Hypophospatemia can be caused by what conditions?

Answer 10

Decreased diet:

• Inadequate intake
• Inhibition of absorption
• Chronic diarrhea
• Vitamin D deficiency

Increased transport into cells

• Increased insulin (refeeding)
• Acute respiratory alkalosis
• Hungry bone syndrome

Increased urine phosphate

• Hyperparathyroidism
• Vitamin D deficiency
• Fanconi syndrome
• Oncogenic osteomalacia

Question 11

What are severe cases of hypophosphatemia characterized (Serum [Pi] < 1.5 mg/dL) by?

Answer 11

Anorexia
Confusion
Rhabdomyolysis
Paralysis
Seizures