Lecture 2 - Disorders of Calcium Homeostatis

Question 1

What is 1^o Hyperparathyroidism?

Answer 1

1^o Hyperparathyroidism is the excess secretion of PTH from a defective parathyroid gland.

Question 2

What is 2^o HPT?

Answer 2

Excess PTH secretion by the parathyroid glands due to chronic renal failure or rickets

Question 3

What is the cause of 1^o HPT?

Answer 3

A monoclonal parathyroid adenoma (hyperplasia)

Question 4

What are the syptoms of 1^o HPT?

Answer 4

• Hypercalcaemia
• Hypophosphatemia
• Bone demineralisation
• Hypercalciuria which results in kidney stones
• Multiple bone cysts (osteitis fibrosa cystica)

Question 5

What could the causes of a parathyroid adenoma which results in 1^o HPT be?

Answer 5

The causes of 1^o HPT could be:

• A mutation in the Vitamin D receptor gene (VDR)
• Mutation of MEN1 (multiple endocrine neoplasia) tumour suppressor gene
• Overexpression of cyclin D1 (cell cycle regulator); implicated in 20-40% sporadic PT adenomas

Question 6

What saying used is used to remember the effects of 1^o HPT?

Answer 6

“Stones, bones, abdominal groans and psychic moans”
This is due to:
-Kidney stones caused by hypocalciuria
-Bone demineralisation
-GI disturbances
-Depression and lethargy

Question 7

How can 1^o Hyperparathyroidism be treated?

Answer 7

1^o Hyperparathyroidism can be treated with a parathyroidectomy.
This is relatively inexpensive and curative.
However if all four parathyroids are removed, Ca²/Vit D replacement is needed for life.

Question 8

What would happen in the absence of Ca²⁺ replacement following a parathyroidectomy of all 4 parathyroid glands?

Answer 8

The serum Ca²⁺ would steadily drop which would result in hypocalcaemic tetany.
Tetany following thyroid surgery indicates inadvertant PTX.

Question 9

What is the main 1^o hyperparathyroid complication and what subsequent dietary recommendations are given?

Answer 9

The main parathyroid complication is nephrolithiasis which requires hydration and moderate Ca²⁺ intake

Question 10

How would a 1^o HPT adenoma be identified?

Answer 10

A 1^o HPT adenoma can be recognised using Technetium 99 and a Sestamibi scan.

After 15 minutes the Tc 99 would be taken up into the thyroid.

After 2-hours, uptake would be concentrated within the parathyroid adenoma

Question 11

What is MIRP?

Answer 11

The procedure for Minimally Invasive Radioguided Parathyroidectomy (MIRP) is as follows:

1) A Tc99-labelled protein selectively labels the parathyroid adenoma. The 3 normal glands label poorly due to high Ca2+ induced inactivity.
2) The preoperative scan shows the surgeon location and the size of the affected gland.
3) Using a radiation sensitive probe the surgeon identifies the labelled tissue and removes it.

Question 12

How is PTH secretion increased?

Answer 12

PTH secretion increases in response to DECREASES in serum Ca²⁺ and INCREASES in serum phosphate (Pi)

Question 13

What occurs in chronic renal failure (CRF)?

Answer 13

In CRF, the kidney fails to excrete sufficient PO₄ and produces little 1,25(OH)₂D_3.

Question 14

Describe the effect which Kidney disease has on phosphate, pH and PTH.

Answer 14

Kidney disease results in hyperphosphataemia, low pH and renders the proximal tubule unresponsive to PTH.

Question 15

What effects do low 1,25(OH)₂D₃ have on Ca²⁺ absorbtion?

Answer 15

Low 1,25(OH)₂D₃ levels decrease gut Ca²⁺ absorbtion

Question 16

What effects result from CRF?

Answer 16

CRF results in 2