Chempath 10: Calcium

Question 1

Where does PTH act ?

Answer 1

• Kidneys directly (increased Ca reabsorption, increased PO4 excretion)
• Increases 1 alpha hydroxylase
• Bone (causes increased Ca and PO4 resorption)

Question 2

What does 1° alpha hydroxylase do ?

Answer 2

Activates vitamin D 25-OH-D3 –> 25- (OH)2-D3

Question 3

What is the most common cause of 1° hyperparathyroidism?

Answer 3

Parathyroid adenoma

Question 4

What causes 2° hyperparathyroidism ?

Answer 4

Renal osteodystrophy

(chronic renal failure means less vitamin D activated, so less Ca resorption and less PO4 excretion. low calcium causes PTH release)

Question 5

What causes 3° hyperparathyroidism ?

Answer 5

Prolonged CKD in 2° hyperparathyroidism causes hyperplasia of the Parathyroid causing autonomous PTH release even when Ca is high.

Question 6

List 2 causes of hypoparathyroidism ?

Answer 6

1- Di George syndrome

2- Post thyroidectomy

Question 7

What does vitamin D deficiency cause ?

Answer 7

Rickets in children

Osteomalacia in adults

Question 8

Which metabolic bone disorder causes looser’s zone fractures and bowing ?

Answer 8

Osteomalacia

Question 9

What happens in Paget’s disease?

Answer 9

Increased bone remodelling

high PTH

Question 10

How can sarcoidosis cause hypercalcaemia ?

Answer 10

causes non-renal release of 1 alpha hydroxylase

Question 11

What are the features of Pseudohypoparathyroidism?

Answer 11

• Type 1a = Albright’s hereditary osteodystrophy
• High PTH, low Ca, High PO4
• PTH resistance means low calcium
• syndromic features: low IQ, short stature, short 4th and 5th metacarpals
• Maternal imprinting of an autosomal dominant mutation

Question 12

What are the features of pseudopseudohypoparathyroidism ?

Answer 12

• same syndromic features as Albright’s hereditary osteodystrophy
• Calcium is normal because no PTH resistance
• Paternal imprinting of autosomal dominant mutation

Question 13

What is the management of hypercalcaemia?

Answer 13

1- Hydration with fluids
2- Bisphosphonates
3- Calcitonin (severe)

Question 14

What is the management of hypocalcaemia ?

Answer 14

1-Give calcium
CKD: Alpha calcidiol
3- 10% Calcium gluconate IV

Question 15

Why can Chronic pancreatitis cause Osteomalacia ?

Answer 15

• Chronic pancreatitis causes a reduction in emulsification of fats
• This means less fat soluble vitamins (ADEK) are absorbed from the G.I tract
• Causing a vitamin D deficiency and therefore osteomalacia

Question 16

Why does Multiple Myeloma not cause a raised ALP ?

Answer 16

• Multiple myeloma only affects osteoclasts

- Osteoblast activity is what releases ALP

Question 17

List 4 causes of a raised ALP?

Answer 17

• Cholestatic liver disease (also raised GGT)
• Pregnancy (Placenta releases ALP)
• Bone disease (Paget’s, Renal osteodystrophy fracture)
• Drugs (carbamazepine, phenytoin, erythromycin)

Question 18

Why do we use corrected calcium ?

Answer 18

-Because normally 40% of calcium is bound to albumin, so if anything affects albumin it would also affect calcium levels.

Corrected calcium takes albumin into consideration

Question 19

List 3 causes of hypocalcaemia with elevated phosphate ?

Answer 19

• CKD
• Hypoparathyroidism
• Hypomagnesaemia
• (Pseudohypoparathyroidism)

Question 20

List 3 causes pf Hypocalcaemia with normal or low phosphate ?

Answer 20

• Osteomalacia
• Acute pancreatitis
• Respiratory alkalosis

Question 21

Why does respiratory alkalosis cause Hypocalcaemia ?

Answer 21

• Respiratory alkalosis is most commonly due to hyper ventilation.
• The alkalosis causes increased binding of free calcium to albumin.
• Less free calcium causes hypocalcaemia seen with symptoms such as parasthesia, tetany etc