Disorders of Calcium and Phosphate Metabolism

Question 1

Where is our main source of calcium from?

Answer 1

Diet

Question 2

What is the main source of calcium removal?

Answer 2

Kidney

Question 3

How does vitamin D act on the gut and bone?

Answer 3

• Gut - increase calcium absorption
• Bone - increase resorption of bone, so inc calcium

Question 4

Which hormones does high calcium inhibit?

Answer 4

PTH and in turn vitamin D

Question 5

Which hormone actively reduces calcium levels?

Answer 5

Calcitonin - produced by C cells of thyroid, inhibits action of PTH on the bone. Stimulates osteoblasts and increases calcium excretion.

Question 6

What hormone level change is responsible for hypercalcaemia?

Answer 6

PTH

Biggest causes of hypercalcaemia = high or low PTH

Question 7

High PTH can cause hypercalcaemia. What is the biggest reason for high PTH?

Answer 7

Vast majority of high PTH cases of hypercalcaemia are due to hyperparathyroidism. Some due to cancer.

Question 8

What are the causes of low PTH?

Answer 8

• Mainly cancer
• Hypervitaminosis D (exogenous, granulamotous disease, will S)
• Increased bone turnover (acromegaly, thyrotoxicosis)

Question 9

Describe differences in diagnosing primary, secondary and teritary hyperparathyroidism and how PTH/calcium levels differ

Answer 9

• Primary = PTH high, calcium high
• Secondary = calcium low/normal, PTH high (overcompensating)
• Tertiary = PTH high, calcium high

Teritary only ever diagnosed if there was an obvious previous case of secondary hyperparathyroidism.

Question 10

Primary hyperparathyroidism is the commonest cause of elevated PTH and calcium levels. What actually causes primary hyperparathyroidism?

Answer 10

• 85% cases are single adenoma
• 15% cases diffuse hyperplasia

< 1% by parathyroid carcinoma

Question 11

What causes secondary hyperparathyroidism?

Answer 11

• Secondary due to hyperfunctioning of parathyroid glands caused by hypocalcaemia/periph resistance to PTH due to:
• > chronic renal insufficiency
• > calcium malabsorption
• > vitamin D deficiency
• > deranged vitamin D metabolism

Question 12

What causes tertiary hyperparathyroidism?

Answer 12

Occurs following previous secondary hyperparathyroidism, in which the glandular hyperfunction continue despite correction of the underlying abnormality
- renal transplanatation

Question 13

One of the hormonal causes of hypercalcaemia of malignancy are metastatic solid tumours. What are the general 4 types?

Answer 13

Lung, breast, kidney, prostate

They enter bone and release calcium into circulation

Question 14

Name 3 granulomatous diseases

Answer 14

• Sarcoidosis
• Tuberculosis
• Berylliosis
• Coccidioidomycosis
• Histoplasmosis

Question 15

How do granulomatous diseases cause hypercalcaemia?

Answer 15

They present with big pathogens, so require macrophages to invade - macrophages express 1-a-hydroxylase and over activate vitamin D causing an increase in Vit D -> results in increased calcium!

Question 16

What do thiazide and loop diuretics do to calcium levels?

Answer 16

Thiazide diuretics block excretion of calcium from the body, so inc calcium in blood whereas loop diuretics decrease calcium in blood.

Question 17

What does “stones, bones and psychic moans” refer to?

Answer 17

Symptoms of hypercalcaemia

• Kidney stones
• Bone aches
• Confusion, memory loss, dementia, depression
• Constipation, nausea, abd pain, peptic ulcer disease

Question 18

How is hypercalcaemia investigated / diagnosed?

Answer 18

• Blood levels -> calcium phosphate
• U&E magnesium
• Vitamin D, PTH
• Urinary calcium excretion
• CXR
• ACE levels
• Myeloma screen

Question 19

In a patient with hyperparathyroidism (high PTH), you want to remove the parathyroid glands. What investigations are carried out?

Answer 19

• DEXA scan to see how much mineral in bone
• sestaMIBI scan to distinguish parathyroid from thyroid gland
• Ultrasound of neck
• USS renal tract

Question 20

What is the treatment of hypercalcaemia?

Answer 20

• Saline rehydration
• Frusemide
• Pamidronate infusion
• Calcitonin
• Prednisolone
• Dialysis (if calcium 4+)

Question 21

What is the treatment for hyperparathyroidism?

Answer 21

• Surgery
• Medical - observe, bisphosphonates
• Calcimimetics - cinacalcet (expensive)

Question 22

What are some conditions associated with low PTH/action hypocalcaemia?

Answer 22

• Hypoparathyroidism
• Pseudo-hypoparathyroidism
• Pseuo-pseudo-hypoparathyroidism

Question 23

What are the two possible causes for primary hypoparathyroidism?

Answer 23

• Congenital
• Autoimmune

Question 24

What are the causes of secondary hypoparathyroidism?

Answer 24

• Neck surgery or trauma
• Radioiodine / radiotherapy
• Neonatal
• Hypo and hyper-magnesemia

Question 25

What causes high PTH hypocalcaemia?

Answer 25

• Vit D deficiency (renal/liver disease)
• Poor dietry Ca
• Malabsorption
• Chelation (where calcium removed eg blood transfusion)

Question 26

What are symptoms and signs of hypocalcaemia?

Answer 26

• Paresthesias
• Laryngospasm
• Bronchospasm
• Tetany
• Seizures
• Chvostek’s sign
• Trousseau’s sign
• Prolongued QT interval on ECG

Question 27

What disease does vitamin D deficiency cause?

Answer 27

Osteomalacia

Question 28

What is severe hypocalcaemia and what is the treatment?

Answer 28

• Carpopedal spasm, fitting, arrhythmia
• Calcium < 1.7 mmol/l
• IV 10ml 10% calcium gluconate diluted in 200ml N saline over 10 mins

Question 29

What is the treatment for vitamin D deficiency?

Answer 29

• Calcium and vitamin D tablets 800-1000IU daily
• Vitamin D injection 300 000U IM every 6 months
• Alpha calcidol 0.25-1mg daily

Question 30

What is pseudohypoparathyroidisim?

Answer 30

• Post-receptor defect of PTH receptor, so PTH resistance
• Low calcium
• High phosphate
• Low Vit D hydroxylation
• High PTH

Question 31

What are characteristics of patients with pseudohypoparathyroidism?

Answer 31

• Body habitus (short, obese, round face)
• Reduced IQ
• Brachydactyly
• Ectopic calcification