Parathyroid

Question 1

What are the two cells of the parathyroid gland?

Answer 1

Chief cells- produce PTH

Oxyphil cells- packed with mitochondria (granular/pink on H and E)

Question 2

What triggers the release of PTH from chief cells of the parathyroid?

Answer 2

Low serum (ionized) calcium levels

not under Hypothalamic-pituitary axis..

Question 3

What is the effect of PTH?

Answer 3

Increase serum calcium

Question 4

How does PTH increase serum calcium levels?

Answer 4

Increase renal tubular reabsorption
Increase vitamin D to its active form
Decrease serum phosphate by increasing urinary excretion
Increase GI calcium absorption

Question 5

What are two causes of hypercalcemia with elevated PTH levels?

Answer 5

Primary Hyperparathyroidism

Familial hypocalciuric hypercalcemia

Question 6

What are a few causes of hypercalcemia with low PTH levels?

Answer 6

Hypercalcemia of malignancy
Vitamin D toxicity
Immobilization
Thiazide diuretics
Granulomatous disease (like sarcoidosis)

Question 7

How can malignancy cause hypercalcemia?

Answer 7

Tumors to the bones –> increased resorption

-or-

Paraneoplastic syndrome: release of parathyroid hormone-related peptide (PTH-RP)

Question 8

What is far and away the most common lesion of the parathyroid gland?

Answer 8

Parathyroid adenoma

Question 9

What is the gene involved in MEN1 syndrome?

Answer 9

MEN1- (parathyroid, pancreas and pituitary)

MEN1 is a tumor suppressor gene

Question 10

What is the gene mutated in MEN2A syndrome?

Answer 10

Activating mutation of RET (tyrosine kinase)

Question 11

What is the genetic mutation associated with familial hypocalciuric hypercalcemia

Answer 11

CASR- AD disorder

Ca2+ sensing receptor gene in the renal tubules

Question 12

What is the half life of PTH? Why is this useful?

Answer 12

3 minutes-

You can remove an parathyroid gland suspected of causing primary hypercalcemia and check the PTH levels. If you got the right one, the levels will drop in half within a few minutes

Question 13

What type of cells are missing from parathyroid adenomas?

Answer 13

Fat

Can occupy up to 30% of adult parathyroid glands

Question 14

Define parathyroid hyperplasia

Answer 14

When the disease affects more than one gland.

Parathyroid adenomas are localized to a single gland

Question 15

What are the clinical manifestations of hypercalcemia?

Answer 15

Painful bones, renal stones, abdominal groans and psychic moans

Osteofibrosis cystica, osteoporosis, nephrolithiasis, nephrocalcinosis, gallstones, PUD, acute pancreatitis, CNS depression, seizures…

Question 16

What is the most common cause of secondary hyperparathyroidism?

Answer 16

Renal failure (often with diabetes)

Question 17

What is secondary hyperparathyroidism?

Answer 17

Process of chronic depression or decrease in calcium that causes compensatory over activity of the parathyroid glands

Question 18

What does renal insufficiency cause secondary hyperparathyroidism?

Answer 18

Renal insufficiency causes decreased phosphate excretion –> hyperphosphatemia –> decreased ionized serum calcium

Question 19

What is tertiary hyperparathyroidism?

Answer 19

Autonomous hyperparathyroidism without symptomatic hypercalcemia- follows chronic hypercalcemia due to secondary hyperparathyroidism (again, often due to renal insufficiency)

Question 20

Which is more common: hyper or hypoparathyroidism?

Answer 20

Hyperparathyroidism is way more common than hypoparathyroidism

Question 21

What is the most important cause of hypoparathyroidism?

Answer 21

Surgically induced

Question 22

With what syndrome can you have congenital absence of parathyroid?

Answer 22

DiGeorge’s Syndrome

Question 23

What are the CNS manifestations of hypoparathyroidism?

Answer 23

Tetany: especially perioral numbness
Chvostek sign: tap along course of facial nerve
Trousseau sign: carpal spasms following occlusion of circulation of the forearm

Mental status change

Question 24

How is the QT interval affected by hypoparathyroidism?

Answer 24

Prolonged QT (with low calcium)