Parathyroid Pathology

Question 1

What is the main function of the parathyroid gland?

Answer 1

Calcium regulation, through PTH.

Question 2

Describe the normal pathology of the parathyroid gland. (Location, functional cell type etc.)

Answer 2

Four glands at periphery of thyroid

• Functional cells = chief cells
  
  • Secrete PTH - released in response to low serum calcium

Question 3

Actions of PTH

Answer 3

• Bone resorption
• Renal tubular resorption of calcium
• Increased conversion of Vit D to active form
• Vitamin D promotes calcium resorption from small intestine

Question 4

What are the acute and chronic causes of hypocalcaemia?

Answer 4

Acute - usually due to damage/removal of parathyroid during thyroid surgery.

Chronic:

• Chronic renal failure
• Vit D deficiency
• Intestinal malabsorption of calcium

Question 5

Symptoms of hypocalcaemia?

Answer 5

Hypocalcaemia = neuromuscular irritability.

Calcium usually blocks sodium channels, without calcium there is lower depolarisation threshold and thus irritability:

CATs go numb

• Convulsions
• Arrhythmias
• Tetany
• Numbness

Question 6

Mechanisms of hypercalcaemia?

Answer 6

Hyperparathyroidism

• Accelerated bone resorption
• Excessive GI absorption
• Decreased renal excretion)

Question 7

How does a disrupted Ca/PO4 homeostasis cause hypercalcaemia?

Answer 7

Retention of phosphate inappropriate actively feedback loop leading to increased PTH secretion.

Occurs in renal failure

Question 8

Clinical manifestations of hypercalcaemia:

Answer 8

“Stones, bones, abdominal groans and psychiatric moans”

• Renal stones
• Bone pain
• Abdo - nausea, vomiting, constipation
• Moans - lethary, fatigue

Question 9

4 classifications of hyperparathyroidism and their meaning

Answer 9

Primary HP - Excess PTH production

• Feedback independent

Secondary HP - Other disease process drives increase in PTH

• Normal feedback mechanisms
• Glands become hyperplastic

Tertiary HP - Autonomous PTH secretion caused by long standing secondary HP

• Abnormal feedback mechanisms
• Autonomous nodule in hyperplastic glands

Ectopic Secretion - PTHrP (PTH-related-protein)

• Malignancy causing secretion
• All 4 glands become atrophic
• Feedback independent

Question 10

Two primary causes of hyperparathyroidism?

Answer 10

PT adenoma

PT hyperplasia

Question 11

How common is hypoparathyroidism?

Answer 11

not at all

Question 12

What is the major cause of hyperparathyroidism?

Answer 12

90% of HP - parathyroid adenoma

Question 13

What is MEN1?

Answer 13

Inherited condition associated with tumours of the endocrine glands- particularly PT.

ASsociated with multiple nodular PT adenoma and familial PT hyperplasia.

Question 14

In terms of how much of the parathyroid gland/s are affected, what is the difference between PT adenoma and PT hyperplasi?

Answer 14

PT adenoma = usually solitary gland affected

PT hyperplasia = usually all glands involved (chief cells)

Question 15

What is the cancer associated with the PT?

Answer 15

Parathyroid carcinoma - tumour of the epithelium, rare.